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1
Høg, Erik. "GIER: A Danish computer from 1961 with a role in the modern revolution of astronomy - II". Proceedings of the International Astronomical Union 12, S330 (aprile 2017): 92–93. http://dx.doi.org/10.1017/s1743921317005336.
Abstract (sommario):
AbstractA Danish computer, GIER, from 1961 played a vital role in the development of a new method for astrometric measurement. This method, photon counting astrometry, ultimately led to two satellites with a significant role in the modern revolution of astronomy. A GIER was installed at the Hamburg Observatory in 1964 where it was used to implement the entirely new method for the measurement of stellar positions by means of a meridian circle, at that time the fundamental instrument of astrometry. An expedition to Perth in Western Australia with the instrument and the computer was a success. This method was also implemented in space in the first ever astrometric satellite Hipparcos launched by ESA in 1989. The Hipparcos results published in 1997 revolutionized astrometry with an impact in all branches of astronomy from the solar system and stellar structure to cosmic distances and the dynamics of the Milky Way. In turn, the results paved the way for a successor, the one million times more powerful Gaia astrometry satellite launched by ESA in 2013. Preparations for a Gaia successor in twenty years are making progress.
2
Zacharias, Norbert, Valeri V. Makarov, Charles T. Finch, Hugh C. Harris, Jeffrey A. Munn e John P. Subasavage. "USNO Bright Star Catalog, Version 1". Astronomical Journal 164, n. 2 (5 luglio 2022): 36. http://dx.doi.org/10.3847/1538-3881/ac686d.
Abstract (sommario):
Abstract The USNO Bright Star Catalog (UBSC) is a new astrometric catalog of the 1423 brightest stars covering the entire sky, which is published online. It is nearly complete to V = 3 mag except for three stellar systems. A combined astrometric solution of the Hipparcos Intermediate Astrometry Data and two dedicated ground-based campaigns in 2013–2020 is the basis for this catalog. The astrometric parameters for each star include position coordinates, parallax, and proper motion components, and their covariances on the Hipparcos mean epoch 1991.25. 64% of the catalog are flagged as known or suspected double or binary stars. UBSC lists 68 stars missing in Gaia EDR3 and another 114 stars without Gaia parallaxes or proper motions. The formal precision achieved for proper motions is comparable to that of Gaia.
3
Brandt, G. Mirek, Daniel Michalik, Timothy D. Brandt, Yiting Li, Trent J. Dupuy e Yunlin Zeng. "htof: A New Open-source Tool for Analyzing Hipparcos, Gaia, and Future Astrometric Missions". Astronomical Journal 162, n. 6 (5 novembre 2021): 230. http://dx.doi.org/10.3847/1538-3881/ac12d0.
Abstract (sommario):
Abstract We present htof, an open-source tool for interpreting and fitting the intermediate astrometric data (IAD) from both the 1997 and 2007 reductions of Hipparcos, the scanning law of Gaia, and future missions such as the Nancy Grace Roman Space Telescope (NGRST). htof solves the astrometric parameters of any system for any arbitrary combination of absolute astrometric missions. In preparation for later Gaia data releases, htof supports arbitrarily high-order astrometric solutions (e.g., five-, seven-, and nine-parameter fits). Using htof, we find that the IAD of 6617 sources in Hipparcos 2007 might have been affected by a data corruption issue. htof integrates an ad hoc correction that reconciles the IAD of these sources with their published catalog solutions. We developed htof to study masses and orbital parameters of substellar companions, and we outline its implementation in one orbit fitting code (orvara). We use htof to predict a range of hypothetical additional planets in the β Pic system, which could be detected by coupling NGRST astrometry with Gaia and Hipparcos. htof is pip installable and available at https://github.com/gmbrandt/htof.
4
Chilcote, Jeffrey, Taylor Tobin, Thayne Currie, Timothy D. Brandt, Tyler D. Groff, Masayuki Kuzuhara, Olivier Guyon et al. "SCExAO/CHARIS Direct Imaging of A Low-mass Companion At A Saturn-like Separation from an Accelerating Young A7 Star". Astronomical Journal 162, n. 6 (19 novembre 2021): 251. http://dx.doi.org/10.3847/1538-3881/ac29ba.
Abstract (sommario):
Abstract We present the SCExAO direct imaging discovery and characterization of a low-mass companion to the nearby young A7IV star, HD 91312. SCExAO/CHARIS JHK (1.1–2.4 μm) spectra and SCExAO/HiCIAO H-band imaging identify the companion over a two year baseline in a highly inclined orbit with a maximum projected separation of 8 au. The companion, HD 91312 B, induces an 8.8σ astrometric acceleration on the star as seen with the Gaia & Hipparcos satellites and a long-term radial-velocity trend as previously identified by Borgniet et al. HD 91312 B’s spectrum is consistent with that of an early-to-mid M dwarf. Hipparcos and Gaia absolute astrometry, radial-velocity data, and SCExAO/CHARIS astrometry constrain its dynamical mass to be 0.337 − 0.044 + 0.042 M ⊙, consistent with - but far more precise than - masses derived from spectroscopy, and favors a nearly edge-on orbit with a semimajor axis of ∼9.7 au. This work is an example of precisely characterizing properties of low-mass companions at solar system-like scales from a combination of direct imaging, astrometry, and radial-velocity methods.
5
Lindegren, L., e M. A. C. Perryman. "Microarcsec Astrometry: The Gaia Mission". Highlights of Astronomy 11, n. 1 (1998): 581–82. http://dx.doi.org/10.1017/s1539299600022401.
Abstract (sommario):
The Hipparcos mission demonstrated the efficiency of space astrometry (in terms of number of objects, accuracy, and uniformity of results) and the fact that a relatively small instrument can have a very large scientific potential in the area of astrometry. However, Hipparcos could probe less than 0.1 per cent of the volume of the Galaxy by direct distance measurements. Using a larger instrument and more efficient detectors, it is now technically feasible to increase the efficiency of a space astrometry mission by several orders of magnitude, thus encompassing a large part of the Galaxy within its horizon for accurate determination of parallaxes and transverse velocities. Such a mission will have immediate and profound impact in the areas of the physics and evolution of individual stars and of the Galaxy as a whole.
6
Sabu, Nidhi, Thomaskutty Francis, Arun Roy e Sreeja S. Kartha. "Gaia: Surveying Heavens". Mapana - Journal of Sciences 17, n. 1 (1 gennaio 2018): 11–23. http://dx.doi.org/10.12723/mjs.44.2.
Abstract (sommario):
In this paper we attempt to study an ongoing astrometry mission of the European Space Agency (ESA), named Gaia, whose aim is to make the largest and most precise three-dimensional map of our Galaxy. We present the scientific goals of Gaia and give a brief description of the spacecraft. We also present a preliminary analysis of comparing distance estimates of Be stars from the first Gaia data release, Gaia DR1, and Hipparcos mission. From our analysis, we confirm that Gaia stands out as a promising mission in terms of the distance measurements when compared to Hipparcos, particularly for distances greater than 1 kpc.
7
Bernstein, H. H. "Derivation of orbital parameters of very low mass companions in double stars from radial velocities and observations of space astrometry missions like HIPPARCOS, DIVA and GAIA". International Astronomical Union Colloquium 170 (1999): 410–15. http://dx.doi.org/10.1017/s0252921100048843.
Abstract (sommario):
AbstractRadial velocity measurements are a well known high-precision method to obtain the orbits of extrasolar planets or brown dwarfs. However, this method is not able to determine the inclination which could be derived from astrometry. The astrometric effects of those objects are very minute, wherefore the interest of astronomers in astrometric techniques was very poor. This situation changes fundamentally since space astrometry observations are available. HIPPARCOS demonstrated the power of space astrometry and the extremely high accuracy of the DIVA, and especially the GAIA observations allows one to detect Jupiter- and Earth- like objects. The optimal estimation of the parameters of the orbit of extrasolar planets or brown dwarfs is a combination of radial velocity measurements and space astrometry observations. Here it is possible to overcome problems which are inherent in both observation methods, so space astrometry complements radial velocity observations and vice versa. This paper gives a method for the parameter estimation using both types of measurements.
8
Scholz, R. D., S. Drew Chojnowski e S. Hubrig. "Strongly magnetic Ap stars in the Gaia DR2 Hertzsprung-Russell diagram". Astronomy & Astrophysics 628 (agosto 2019): A81. http://dx.doi.org/10.1051/0004-6361/201935752.
Abstract (sommario):
Context. Knowing the distribution of strongly magnetic Ap stars in the Hertzsprung-Russell diagram (HRD) allows us to study the evolution of their magnetic fields across the main sequence (MS). With a newly extended Ap star sample from APOGEE and available Gaia DR2 data, we can now critically review the results of previous studies based on HIPPARCOS data. Aims. To investigate our targets in the Gaia DR2 HRD, we need to define astrometric and photometric quality criteria to remove unreliable data from the HRD. Methods. We used the Gaia DR2 renormalised unit weight error RUWE as our main quality criterion. We considered known (close) binaries in our sample compared to their (partly affected) astrometry and used the Gaia DR2 data to find common parallax and proper motion (CPPM) wide companions and open cluster members. We studied G, BP, and RP variability amplitudes and their significance as a function of magnitude. In colour-magnitude diagrams (CMDs) with absolute G magnitude (determined from inverted parallax) versus BP − RP colour and HRDs, where BP − RP is replaced by effective temperature, we studied the appearance of outliers with respect to their astrometric quality, binarity, and variability. Results. We present a catalogue of 83 previously known and 154 new strongly magnetic Ap stars with Gaia DR2 data, including astrometric quality parameters, binary flags, information on cluster membership, variability amplitudes, and data from HIPPARCOS. Our astrometrically cleaned subsamples include 47 and 46 old and new Ap stars with parallaxes > 2 mas. Most of the known 26 binaries among all 237 stars and 14 out of 15 CMD/HRD outliers were excluded by astrometric criteria. The remaining 11 known binaries and a few highly variable objects mainly appear in the bright and red CMD/HRD parts. A CMD based on HIPPARCOS photometry and Gaia DR2 parallaxes shows a much more narrow distribution in the absolute V magnitudes of 75 common Ap stars over the full B − V colour range than the corresponding CMD based on HIPPARCOS parallaxes.
9
Röser, S., U. Bastian, K. S. de Boer, E. Høg, E. Schilbach, CH de Vegt e S. Wagner. "Diva - A Small Satellite for Global Astrometry and Photometry". Highlights of Astronomy 11, n. 1 (1998): 583. http://dx.doi.org/10.1017/s1539299600022413.
Abstract (sommario):
DIVA (Double Interferometer for Visual Astrometry) is a Fizeau interferometer on a small satellite. It will perform astrometric and photometric observations of at least 4 million stars. A launch in 2002 and a minimum mission length of 24 months are aimed at. A detailed description of the experiment can be obtained from the DIVA homepage at http://www.aip.de:8080/dso/diva. An overview is given by Röser et al., 1997.The limiting magnitude of DIVA is about V = 15 for spectral types earlier than M0, but drops to about V = 17.5 for stars later than M5. Table 1 gives a short overview on DIVA’s performance. DIVA will carry out a skysurvey complete to V = 12.5. For the first time this survey will comprise precise photometry in at least 8 bands in the wavelength range from 400 to 1000 nm.DIVA will improve parallaxes by a factor of 3 compared to Hipparcos; proper motions by at least a factor of 2 and, in combination with the Hipparcos observations, by a factor of 10 for Hipparcos stars. At least 30 times asmany stars as Hipparcos will be observed, and doing this DIVA will fill the gap in observations between Hipparcos and GAIA. DIVA’s combined astrometric and photometric measurements of high precision will have important impacts on astronomy and astrophysics in the next decade.
10
Lindegren, Lennart, e Dainis Dravins. "Astrometric radial velocities for nearby stars". Astronomy & Astrophysics 652 (agosto 2021): A45. http://dx.doi.org/10.1051/0004-6361/202141344.
Abstract (sommario):
Context. Under certain conditions, stellar radial velocities can be determined from astrometry, without any use of spectroscopy. This enables us to identify phenomena, other than the Doppler effect, that are displacing spectral lines. Aims. The change of stellar proper motions over time (perspective acceleration) is used to determine radial velocities from accurate astrometric data, which are now available from the Gaia and HIPPARCOS missions. Methods. Positions and proper motions at the epoch of HIPPARCOS are compared with values propagated back from the epoch of the Gaia Early Data Release 3. This propagation depends on the radial velocity, which obtains its value from an optimal fit assuming uniform space motion relative to the solar system barycentre. Results. For 930 nearby stars we obtain astrometric radial velocities with formal uncertainties better than 100 km s−1; for 55 stars the uncertainty is below 10 km s−1, and for seven it is below 1 km s−1. Most stars that are not components of double or multiple systems show good agreement with available spectroscopic radial velocities. Conclusions. Astrometry offers geometric methods to determine stellar radial velocity, irrespective of complexities in stellar spectra. This enables us to segregate wavelength displacements caused by the radial motion of the stellar centre-of-mass from those induced by other effects, such as gravitational redshifts in white dwarfs.
11
Brown, Anthony G. A. "Microarcsecond Astrometry: Science Highlights from Gaia". Annual Review of Astronomy and Astrophysics 59, n. 1 (8 settembre 2021): 59–115. http://dx.doi.org/10.1146/annurev-astro-112320-035628.
Abstract (sommario):
Access to microarcsecond astrometry is now routine in the radio, infrared (IR), and optical domains. In particular, the publication of the second data release ( Gaia DR2) from the Gaia mission made it possible for every astronomer to work with easily accessible, high-precision astrometry for 1.7 billion sources to twenty-first magnitude over the full sky. ▪ Gaia provides splendid astrometry, but at the limits of the data small systematic errors are present. A good understanding of the Hipparcos– Gaia astrometry concept, and of the data collection and processing, provides insights into the origins of the systematic errors and how to mitigate their effects. ▪ A selected set of results from Gaia highlight the breadth of exciting science and unexpected results, from the Solar System to the distant Universe, to creative uses of the data. ▪ Gaia data release 2 provides, for the first time, a dense sampling of Galactic phase space with high-precision astrometry, photometry, and radial velocities, allowing researchers to uncover subtle features in phase space and the observational Hertzsprung–Russell diagram. ▪ In the coming decade, we can look forward to more accurate and richer Gaia data releases, and new photometric and spectroscopic surveys coming online that will provide essential complementary data. ▪ The longer term promises exciting new opportunities for microarcsecond astrometry and beyond, including the plans for an IR version of Gaia that would offer the dense sampling of phase space deep into the Milky Way's nuclear regions.
12
Michalik, Daniel, Lennart Lindegren, David Hobbs, Uwe Lammers e Yoshiyuki Yamada. "Improving distance estimates to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia". Proceedings of the International Astronomical Union 8, S289 (agosto 2012): 414–17. http://dx.doi.org/10.1017/s1743921312021849.
Abstract (sommario):
AbstractStarting in 2013, Gaia will deliver highly accurate astrometric data, which eventually will supersede most other stellar catalogues in accuracy and completeness. It is, however, limited to observations from magnitude 6 to 20 and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall Japanese astrometry satellite, will observe these bright stars, but with much lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the main source of accurate distances to bright nearby stars. We are investigating how this might be improved by optimally combining data from all three missions through a joint astrometric solution. This would take advantage of the unique features of each mission: the historic bright-star measurements of Hipparcos, the updated bright-star observations of Nano-JASMINE, and the very accurate reference frame of Gaia. The long temporal baseline between the missions provides additional benefits for the determination of proper motions and binary detection, which indirectly improve the parallax determination further. We present a quantitative analysis of the expected gains based on simulated data for all three missions.
13
Seidelmann, P. K. "Prospects for Future Astrometric Missions". Symposium - International Astronomical Union 179 (1998): 79–85. http://dx.doi.org/10.1017/s0074180900128232.
Abstract (sommario):
Hipparcos and the Hubble Space Telescope have demonstrated the astrometric capabilities in space. SIM and GAIA are being studied for future missions. There have been many proposals for new astrometry missions from many different countries, but most of them have not been funded.The best possibility for a mission within the next five years would be through a collaborative effort for a small, fast, cheap spacecraft which could be a precursor for future, larger, more accurate missions, which are under study.
14
Johnston, Kenneth J. "The Future of Space Astrometry". International Astronomical Union Colloquium 180 (marzo 2000): 392–97. http://dx.doi.org/10.1017/s0252921100000543.
Abstract (sommario):
AbstractThe future of space-based astrometric missions appears to be very promising. Three missions were described at IAU Colloquium 180. These are the Full-sky Astrometric Mapping Explorer (FAME), the Space Interferometry Mission (SIM) and the Global Astrometric Interferometer for Astrophysics (GAIA) missions. These missions will substantially improve the accuracy of global astrometric measurements made by the Hipparcos space mission by factors of 20 to 250. A brief summary of these projects is given.
15
Høg, E. "From the Roemer mission to Gaia". Proceedings of the International Astronomical Union 3, S248 (ottobre 2007): 300–302. http://dx.doi.org/10.1017/s1743921308019418.
Abstract (sommario):
AbstractAt the IAU symposium in Shanghai September 1992 the present author made the first proposal for a specific mission concept post-Hipparcos, the first scanning astrometry mission with CCDs in time-delayed integration mode (TDI). Direct imaging on CCDs in long-focus telescopes was described as later adopted for the Gaia mission. The mission called Roemer was designed to provide accurate astrometry and multi-colour photometry of 400 million stars brighter than 18 mag in a five-year mission. The early years of this mission concept are reviewed.
16
Kumar, Sangeeta, e Maïssa Salama. "A Report on Stellar Companion Mass Estimates within Our Solar Neighborhood". Research Notes of the AAS 8, n. 5 (3 maggio 2024): 123. http://dx.doi.org/10.3847/2515-5172/ad4608.
Abstract (sommario):
Abstract We present mass estimates and companion demographics on stellar multiples within 25 pc, using a survey of stars of all spectral types done by Robo-AO and supplemented by Gaia. The survey combined direct imaging by Robo-AO, a robotic adaptive optics instrument for 2 m class telescopes, to detect tight companions (<4″ separation) and with Gaia astrometry to detect wider co-moving companions. We estimated the masses for 267 companions using empirical relations and, for a subset of 97, dynamical mass estimates. We utilized previous mass–magnitude models using contrasts measured from Gaia and Robo-AO to estimate the mass and also used the orvara python package, a Markov Chain Monte Carlo orbit fitter using the companion astrometry and Hipparcos-Gaia proper motion accelerations, to estimate dynamical masses. We compare agreements and discrepancies in mass estimates from these two methods.
17
Hobbs, David, e Erik Høg. "GaiaNIR – A future all-sky astrometry mission". Proceedings of the International Astronomical Union 12, S330 (aprile 2017): 67–70. http://dx.doi.org/10.1017/s1743921317005348.
Abstract (sommario):
AbstractWith the launch of Gaia in December 2013, Europe entered a new era of space astrometry following in the footsteps of the very successful Hipparcos mission. A weakness of Gaia is that it only operates at optical wavelengths. However, much of the Galactic centre and the spiral arm regions are obscured by interstellar extinction. An obvious improvement on Gaia is to include the Near-Infra-Red (NIR) which requires the use of new types of detectors. Additionally, to scan the entire sky and measure global absolute parallaxes the spacecraft must have a constant rotation resulting in a moving image that must be compensated for by, for example, operating the detectors in Time Delayed Integration (TDI) mode. If these technical issues can be solved a new Gaia-like mission separated by a 20 year interval would give; 1) NIR all-sky astrometry and photometry to penetrate the obscured regions and to observe intrinsically red objects with almost diffraction limited resolution; 2) improved proper motions with fourteen times smaller errors than from Gaia alone opening up new science cases, such as long period exoplanets and accurate halo measurements; 3) allow the slowly degrading accuracy of the Gaia reference frame, which will be the basis for future astronomical measurements, to be reset.
18
Makarov, V. V. "THE HIPPARCOS PLEIADES PARALLAX ERROR IS ALSO A PROPER MOTION ERROR". Revista Mexicana de Astronomía y Astrofísica 58, n. 2 (1 ottobre 2022): 315–20. http://dx.doi.org/10.22201/ia.01851101p.2022.58.02.12.
Abstract (sommario):
The mean parallax of the Pleiades open cluster from the Hipparcos catalog is larger than the true value by approximately 1 mas. The origin of this error, as well as a possible algorithm of correcting it, was proposed by Makarov (2002). The problem is reassessed using the more accurate Gaia data with a focus on the predicted correction to the Pleiades proper motions. The accurately determined differences Gaia − Hipparcos for 52 common stars are close to these estimates within the formal uncertainties for all three parameters, which strongly suggests that the proposed interpretation was correct. With adjustments for the systematic vector field fitted with 126 vector spherical harmonics to degree 7, these differences amount to (+0.39, −0.74) mas yr−1 . The implications of small-scale proper motion and position errors in Hipparcos for present day astrometry are briefly discussed.
19
Poggio, E., R. Drimmel, R. L. Smart, A. Spagna e M. G. Lattanzi. "Search for Galactic warp signal in Gaia DR1 proper motions". Proceedings of the International Astronomical Union 12, S330 (aprile 2017): 185–88. http://dx.doi.org/10.1017/s1743921317006032.
Abstract (sommario):
AbstractThe nature and origin of the Galactic warp represent one of the open questions posed by Galactic evolution. Thanks to Gaia high precision absolute astrometry, steps towards the understanding of the warp's dynamical nature can be made. Indeed, proper motions for long-lived stable warp are expected to show measurable trends in the component vertical to the galactic plane. Within this context, we search for the kinematic warp signal in the first Gaia data release (DR1). By analyzing distant spectroscopically-identified OB stars in the Hipparcos subset in Gaia DR1, we find that the kinematic trends cannot be explained by a simple model of a long-lived warp. We therefore discuss possible scenarios for the interpretation of the obtained results. We also present current work in progress to select a larger sample of OB star candidates from the Tycho-Gaia Astrometric Solution (TGAS) subsample in DR1, and delineate the points that we will be addressing in the near future.
20
Hodgkin, Simon T., Łukasz Wyrzykowski, Nadejda Blagorodnova e Sergey Koposov. "Transient astronomy with the Gaia satellite". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, n. 1992 (13 giugno 2013): 20120239. http://dx.doi.org/10.1098/rsta.2012.0239.
Abstract (sommario):
Gaia is a cornerstone European Space Agency astrometry space mission and a successor to the Hipparcos mission. Gaia will observe the whole sky for 5 years, providing a serendipitous opportunity for the discovery of large numbers of transient and anomalous events, e.g. supernovae, novae and microlensing events, gamma-ray burst afterglows, fallback supernovae, as well as theoretical or unexpected phenomena. In this paper, we discuss our preparations to use Gaia to search for transients at optical wavelengths, and briefly describe the early detection, classification and prompt publication of anomalous sources.
21
Grandjean, A., A. M. Lagrange, H. Beust, L. Rodet, J. Milli, P. Rubini, C. Babusiaux et al. "Constraining the properties of HD 206893 B". Astronomy & Astrophysics 627 (luglio 2019): L9. http://dx.doi.org/10.1051/0004-6361/201935044.
Abstract (sommario):
Context. High contrast imaging enables the determination of orbital parameters for substellar companions (planets, brown dwarfs) from the observed relative astrometry and the estimation of model and age-dependent masses from their observed magnitudes or spectra. Combining astrometric positions with radial velocity gives direct constraints on the orbit and on the dynamical masses of companions. A brown dwarf was discovered with the VLT/SPHERE instrument at the Very Large Telescope (VLT) in 2017, which orbits at ∼11 au around HD 206893. Its mass was estimated between 12 and 50 MJ from evolutionary models and its photometry. However, given the significant uncertainty on the age of the system and the peculiar spectrophotometric properties of the companion, this mass is not well constrained. Aims. We aim at constraining the orbit and dynamical mass of HD 206893 B. Methods. We combined radial velocity data obtained with HARPS spectra and astrometric data obtained with the high contrast imaging VLT/SPHERE and VLT/NaCo instruments, with a time baseline less than three years. We then combined those data with astrometry data obtained by HIPPARCOS and Gaia with a time baseline of 24 yr. We used a Markov chain Monte Carlo approach to estimate the orbital parameters and dynamical mass of the brown dwarf from those data. Results. We infer a period between 21 and 33 yr and an inclination in the range 20−41° from pole-on from HD 206893 B relative astrometry. The RV data show a significant RV drift over 1.6 yr. We show that HD 206893 B cannot be the source of this observed RV drift as it would lead to a dynamical mass inconsistent with its photometry and spectra and with HIPPARCOS and Gaia data. An additional inner (semimajor axis in the range 1.4–2.6 au) and massive (∼15 MJ) companion is needed to explain the RV drift, which is compatible with the available astrometric data of the star, as well as with the VLT/SPHERE and VLT/NaCo nondetection.
22
Tobin, Taylor L., Thayne Currie, Yiting Li, Jeffrey Chilcote, Timothy D. Brandt, Brianna Lacy, Masayuki Kuzuhara et al. "Direct-imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star HIP 39017". Astronomical Journal 167, n. 5 (9 aprile 2024): 205. http://dx.doi.org/10.3847/1538-3881/ad3077.
Abstract (sommario):
Abstract We present the direct-imaging discovery of a substellar companion (a massive planet or low-mass brown dwarf) to the young, γ Doradus (γ Dor)-type variable star HIP 39017 (HD 65526). The companion’s SCExAO/CHARIS JHK (1.1–2.4 μm) spectrum and Keck/NIRC2 L ′ photometry indicate that it is an L/T transition object. A comparison of the JHK+L ′ spectrum to several atmospheric model grids finds a significantly better fit to cloudy models than cloudless models. Orbit modeling with relative astrometry and precision stellar astrometry from Hipparcos and Gaia yields a semimajor axis of 23.8 − 6.1 + 8.7 au, a dynamical companion mass of 30 − 12 + 31 M J, and a mass ratio of ∼1.9%, properties most consistent with low-mass brown dwarfs. However, its mass estimated from luminosity models is a lower ∼13.8 M J due to an estimated young age (≲115 Myr); using a weighted posterior distribution informed by conservative mass constraints from luminosity evolutionary models yields a lower dynamical mass of 23.6 − 7.4 + 9.1 M J and a mass ratio of ∼1.4%. Analysis of the host star’s multifrequency γ Dor-type pulsations, astrometric monitoring of HIP 39017 b, and Gaia Data Release 4 astrometry of the star will clarify the system age and better constrain the mass and orbit of the companion. This discovery further reinforces the improved efficiency of targeted direct-imaging campaigns informed by long-baseline, precision stellar astrometry.
23
Wyrzykowski, Łukasz, e Simon Hodgkin. "Around Gaia Alerts in 20 questions". Proceedings of the International Astronomical Union 7, S285 (settembre 2011): 425–28. http://dx.doi.org/10.1017/s1743921312001305.
Abstract (sommario):
AbstractGaia is a European Space Agency (ESA) astrometry space mission, and a successor to the ESA Hipparcos mission. Gaia's main goal is to collect high-precision astrometric data (positions, parallaxes, and proper motions) for the 1 billion brightest objects in the sky. Those data, complemented with multi-band, multi-epoch photometric and spectroscopic data observed from the same observing platform, will allow astronomers to reconstruct the formation history, structure, and evolution of the Galaxy.Gaia will observe the whole sky for 5 years, providing a unique opportunity for the discovery of large numbers of transient and anomalous events such as supernovæ, novæ and microlensing events, GRB afterglows, fallback supernovæ, and other theoretical or unexpected phenomena. The Photometric Science Alerts team has been tasked with the early detection, classification and prompt release of anomalous sources in the Gaia data stream. In this paper we discuss the challenges we face in preparing to use Gaia to search for transient pheonomena at optical wavelengths.
24
Benedict, G. F., B. E. McArthur, E. P. Nelan e J. L. Bean. "The 14 Her Planetary System: Companion Masses and Architecture from Radial Velocities and Astrometry". Astronomical Journal 166, n. 1 (26 giugno 2023): 27. http://dx.doi.org/10.3847/1538-3881/acd93a.
Abstract (sommario):
Abstract We combine Hubble Space Telescope (HST) Fine Guidance Sensor, Hipparcos, and Gaia DR3 astrometric observations of the K0 V star 14 Her with the results of an analysis of extensive ground-based radial velocity data to determine perturbation orbits and masses for two previously known companions, 14 Her b and c. Radial velocities obtained with the Hobby–Eberly Telescope and from the literature now span over 25 years. With these data we obtain improved radial velocity (RV) orbital elements for both the inner companion, 14 Her b and the long-period outer companion, 14 Her c. We also find evidence of an additional RV signal with P ∼ 3789d. We then model astrometry from Hipparcos, HST, and Gaia with RV results to obtain system parallax and proper motion, perturbation periods, inclinations, and sizes due to 14 Her b and c. We find P b = 1767.6 ± 0.2 days, perturbation semimajor axis α b = 1.3 ± 0.1 mas, and inclination i b = 36° ± 3°, P c = 52160 ± 1028 days, perturbation semimajor axis α c = 10.3 ± 0.7 mas, and inclination i c = 82° ± 14°. In agreement with a past investigation, the 14 Her b, c orbits exhibit significant mutual inclination. Assuming a primary mass M * = 0.98 ± 0.04M ☉, we obtain companion masses b = 8.5 − 0.8 + 1.0 Jup and c = 7.1 − 0.6 + 1.0 Jup .
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Wagner, S. J., W. Seifert, H. Mandel, U. Bastian e S. RÖser. "The Instrument of the Astrometric Mission Diva". Highlights of Astronomy 11, n. 1 (1998): 584. http://dx.doi.org/10.1017/s1539299600022437.
Abstract (sommario):
As a follow-up to the most successful Hipparcos mission we have suggested a mini-satellite. The instrument DIVA is a pair of two small Fizeau interferometers with a fixed angular separation scanning the entire sky in a Hipparcos-type fashion. Despite its small apertures the very efficient opticaldesign and the use of CCD detectors will allow a significant increase in performance compared to the Hipparcos mission. Introducing objective prisms in front of the beam combiners will generate dispersed fringes which will allow a more accurate astrometry and much more detailed spectro-photometric information than filtered, undispered fringes. A complete optical system was designed which is suitable to achieve the desired goal and may be expanded to the size of GAIA. Likewise, several options exists to improve the capabilities and the depth of the DIVA mission.
26
Turon, C., e F. Arenou. "The Hipparcos Catalogue: 10th anniversary and its legacy". Proceedings of the International Astronomical Union 3, S248 (ottobre 2007): 1–7. http://dx.doi.org/10.1017/s1743921308018516.
Abstract (sommario):
AbstractThe European Space Agency decision to include the Hipparcos satellite into its Science Programme is placed in the context of the years 1965-1980 and in the historical perspective of the progress of astrometry. The motivation and ideas which lead to the Hipparcos design are reviewed as well as its characteristics and performance. The amount and variety of applications represent an impressive evolution from the original science case and opened the way to much more ambitious further space missions, especially Gaia, based on the same basic principles. A giant step in technology led to a giant step in science. Next steps are presented at this Symposium.
27
Munn, Jeffrey A., John P. Subasavage, Hugh C. Harris e Trudy M. Tilleman. "Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database". Astronomical Journal 163, n. 3 (15 febbraio 2022): 131. http://dx.doi.org/10.3847/1538-3881/ac41d2.
Abstract (sommario):
Abstract We present the United States Naval Observatory (USNO) Bright-star Astrometric Database (UBAD), a current-epoch high-accuracy astrometric catalog. The catalog consists of 364 bright northern hemisphere stars, including all but five such stars with either V < 3.5 or with I < 3.2 and V < 6, as well as a large fraction of slightly fainter stars; 36 of the brightest catalog stars are not included in Gaia Early Data Release 3 (EDR3). Observations were conducted with the USNO Flagstaff Station Kaj Strand 61 inch Astrometric Reflector. Target stars were imaged through a small 12.5 mag neutral-density spot, while the remainder of the stars in the field of view were unattenuated. This allowed for unsaturated images of the bright target stars to be calibrated directly against much fainter reference stars from Gaia EDR3. The median position errors are 1.9 mas in both R.A. and decl. at the catalog epoch of 2017.0, with 90% of catalog stars having errors less than 2.6 mas; systematic errors are 1–3 mas. Combining UBAD observations with Hipparcos-2 positions yields proper motions with median errors of 0.045 and 0.049 mas yr−1 in R.A. and decl., respectively, with 90% of stars having errors less than 0.1 mas yr−1; systematic errors are about 0.1 mas yr−1. Single-frame accuracy for positions of the target stars is typically 5–6 mas. Gaia EDR3 astrometry for these bright stars, which are heavily saturated in the Gaia observations, is validated over the magnitude range 2 ≲ G ≲ 6.
28
Feng, Fabo, R. Paul Butler, Hugh R. A. Jones, Mark W. Phillips, Steven S. Vogt, Rebecca Oppenheimer, Bradford Holden, Jennifer Burt e Alan P. Boss. "Optimized modelling of Gaia–Hipparcos astrometry for the detection of the smallest cold Jupiter and confirmation of seven low-mass companions". Monthly Notices of the Royal Astronomical Society 507, n. 2 (3 agosto 2021): 2856–68. http://dx.doi.org/10.1093/mnras/stab2225.
Abstract (sommario):
ABSTRACT To fully constrain the orbits of low-mass circumstellar companions, we conduct combined analyses of the radial velocity data and the Gaia and Hipparcos astrometric data for eight nearby systems. Our study shows that companion-induced position and proper motion differences between Gaia and Hipparcos are significant enough to constrain orbits of low-mass companions to a precision comparable with previous combined analyses of direct imaging and radial velocity data. We find that our method is robust to whether we use Gaia Data Release 2 or Gaia Early Data Release 3, as well as whether we use all of the data or just proper motion differences. In particular, we fully characterize the orbits of HD 190360 b and HD 16160 C for the first time. With a mass of 1.8 ± 0.2 MJup and an effective temperature of 123–176 K and orbiting around a Sun-like star, HD 190360 b is the smallest Jupiter-like planet with well-constrained mass and orbit, belonging to a small sample of fully characterized Jupiter analogues. It is separated from its primary star by 0.25 arcsec and thus may be suitable for direct imaging by the coronagraph instrument of the Roman Space Telescope.
29
Clementini, G., L. Eyer, V. Ripepi, M. Marconi, T. Muraveva, A. Garofalo, L. M. Sarro et al. "Gaia Data Release 1". Astronomy & Astrophysics 605 (settembre 2017): A79. http://dx.doi.org/10.1051/0004-6361/201629925.
Abstract (sommario):
Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims. In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, which involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity (PL), period-Wesenheit (PW) relations for classical and Type II Cepheids and infrared PL, PL-metallicity (PLZ), and optical luminosity-metallicity (MV-[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS. Methods. Classical Cepheids were carefully selected in order to discard known or suspected binary systems. The final sample comprises 102 fundamental mode pulsators with periods ranging from 1.68 to 51.66 days (of which 33 with σϖ/ϖ< 0.5). The Type II Cepheids include a total of 26 W Virginis and BL Herculis stars spanning the period range from 1.16 to 30.00 days (of which only 7 with σϖ/ϖ< 0.5). The RR Lyrae stars include 200 sources with pulsation period ranging from 0.27 to 0.80 days (of which 112 with σϖ/ϖ< 0.5). The new relations were computed using multi-band (V,I,J,Ks) photometry and spectroscopic metal abundances available in the literature, and by applying three alternative approaches: (i) linear least-squares fitting of the absolute magnitudes inferred from direct transformation of the TGAS parallaxes; (ii) adopting astrometry-based luminosities; and (iii) using a Bayesian fitting approach. The last two methods work in parallax space where parallaxes are used directly, thus maintaining symmetrical errors and allowing negative parallaxes to be used. The TGAS-based PL,PW,PLZ, and MV− [Fe/H] relations are discussed by comparing the distance to the Large Magellanic Cloud provided by different types of pulsating stars and alternative fitting methods. Results. Good agreement is found from direct comparison of the parallaxes of RR Lyrae stars for which both TGAS and HST measurements are available. Similarly, very good agreement is found between the TGAS values and the parallaxes inferred from the absolute magnitudes of Cepheids and RR Lyrae stars analysed with the Baade-Wesselink method. TGAS values also compare favourably with the parallaxes inferred by theoretical model fitting of the multi-band light curves for two of the three classical Cepheids and one RR Lyrae star, which were analysed with this technique in our samples. The K-band PL relations show the significant improvement of the TGAS parallaxes for Cepheids and RR Lyrae stars with respect to the Hipparcos measurements. This is particularly true for the RR Lyrae stars for which improvement in quality and statistics is impressive. Conclusions. TGAS parallaxes bring a significant added value to the previous Hipparcos estimates. The relations presented in this paper represent the first Gaia-calibrated relations and form a work-in-progress milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia Data Release 2 (DR2) in 2018.
30
Zhang 张, Jingwen 婧雯, Lauren M. Weiss, Daniel Huber, Eric L. N. Jensen, Timothy D. Brandt, Karen Collins, Dennis M. Conti et al. "Dynamical Architectures of S-type Transiting Planets in Binaries. I. Target Selection Using Hipparcos and Gaia Proper Motion Anomalies*". Astronomical Journal 167, n. 3 (2 febbraio 2024): 89. http://dx.doi.org/10.3847/1538-3881/ad1189.
Abstract (sommario):
Abstract The effect of stellar multiplicity on planetary architecture and orbital dynamics provides an important context for exoplanet demographics. We present a volume-limited catalog of up to 300 pc of 66 stars hosting planets and planet candidates from Kepler, K2, and TESS with significant Hipparcos-Gaia proper motion anomalies, which indicates the presence of companions. We assess the reliability of each transiting planet candidate using ground-based follow-up observations, and find that the TESS Objects of Interest (TOIs) with significant proper anomalies show nearly four times more false positives due to eclipsing binaries compared to TOIs with marginal proper anomalies. In addition, we find tentative evidence that orbital periods of planets orbiting TOIs with significant proper anomalies are shorter than those orbiting TOIs without significant proper anomalies, consistent with the scenario that stellar companions can truncate planet-forming disks. Furthermore, TOIs with significant proper anomalies exhibit lower Gaia differential velocities in comparison to field stars with significant proper anomalies, suggesting that planets are more likely to form in binary systems with low-mass substellar companions or stellar companions at wider separation. Finally, we characterize the three-dimensional architecture of LTT 1445 ABC using radial velocities, absolute astrometry from Gaia and Hipparcos, and relative astrometry from imaging. Our analysis reveals that LTT 1445 is a nearly flat system, with a mutual inclination of ∼2.°88 between the orbit of BC around A and that of C around B. This coplanarity may explain why multiple planets around LTT 1445 A survive in the dynamically hostile environments of this system.
31
Makarov, Valeri V. "MASS RATIOS OF LONG-PERIOD BINARY STARS RESOLVED IN PRECISION ASTROMETRY CATALOGS OF TWO EPOCHS". Revista Mexicana de Astronomía y Astrofísica 57, n. 2 (1 ottobre 2021): 399–405. http://dx.doi.org/10.22201/ia.01851101p.2021.57.02.12.
Abstract (sommario):
Mass ratios of widely separated, long-period, resolved binary stars can be directly estimated from the available data in major space astrometry catalogs, such as the ESA's Hipparcos and Gaia mission results. The method is based on the universal principle of inertial motion of the system's center of mass in the absence of external forces, and is independent of any assumptions about the physical parameters or stellar models. The application is limited by the precision of input astrometric data, the orbital period and distance to the system, and possible presence of other attractors in the vicinity, such as in triple systems. A generalization of this technique to triples is proposed, as well as approaches to estimation of uncertainties. The known long-period binary HIP 473 AB is discussed as an application example, for which a m2/ m1 = 0.996+0.026 −0.026 is obtained.
32
Thejll, P. "Late Stages of Stellar Evolution". Symposium - International Astronomical Union 166 (1995): 173–80. http://dx.doi.org/10.1017/s0074180900228039.
Abstract (sommario):
A review is given of the use of high-accuracy astrometry on research on white dwarfs and the hot subdwarfs and central stars of planetary nebulae (CSPN). Predictions are made about the expected impact of HIPPARCOS, and the possible impacts of GAIA and ROEMER. Discovery of large numbers of new white dwarfs is expected, and, for the more distant hot subdwarfs and CSPN, important refinements of our current understanding of these objects. For white dwarfs independent values of mass and radius may be accurate enough to allow new understanding of the internal composition.
33
Vecchiato, Alberto, Ummi Abbas, Beatrice Bucciarelli, Mario G. Lattanzi e Roberto Morbidelli. "Global astrometric sphere reconstruction in Gaia: challenges and first results of the Verification Unit". Proceedings of the International Astronomical Union 5, S261 (aprile 2009): 337–41. http://dx.doi.org/10.1017/s1743921309990615.
Abstract (sommario):
AbstractGaia will estimate the astrometric and physical data of approximately one billion objects. The core of this process, the global sphere reconstruction, is represented by the reduction of a subset of these objects, which will constitute the largest and most precise catalog of absolute astrometry in the history of Astronomy, and will put General Relativity to test by estimating the PPN parameter γ with unprecedented accuracy. As the Hipparcos mission showed, and as it is natural for all kind of absolute measurements, possible errors in the data reduction can hardly be identified at the end of the processing, and can lead to systematic errors in all the works which will use these results. In order to avoid such kind of problems, a Verification Unit was established by the Gaia Data Processing and Analysis Consortium (DPAC). One of its jobs is to implement and perform an independent global sphere reconstruction, parallel to the baseline one, to compare the two results, and to report any significant difference.
34
Prusti, T. "Gaia: A Stereoscopic Census of Our Galaxy". Proceedings of the International Astronomical Union 5, H15 (novembre 2009): 816. http://dx.doi.org/10.1017/s1743921310011944.
Abstract (sommario):
AbstractGaia is a space astrometry mission, a broad survey project following the measurement and operational principles of Hipparcos. It will help solving one of the most difficult yet deeply fundamental challenges in modern astronomy: to create an extraordinarily precise three-dimensional map of about one billion stars throughout our Galaxy and beyond. In the process, it will map their three-dimensional motions, which encode the origin and subsequent evolution of the Galaxy. Through comprehensive photometric and spectroscopic classification, it will provide the detailed physical properties of each star observed: characterising their luminosity, temperature, gravity, and elemental composition. This massive stellar census will provide the basic observational data to tackle an enormous range of important problems related to the origin, structure, and evolutionary history of our Galaxy.
35
Brandt, G. Mirek, Trent J. Dupuy, Yiting Li, Minghan Chen, Timothy D. Brandt, Tin Long Sunny Wong, Thayne Currie et al. "Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3". Astronomical Journal 162, n. 6 (1 dicembre 2021): 301. http://dx.doi.org/10.3847/1538-3881/ac273e.
Abstract (sommario):
Abstract We present comprehensive orbital analyses and dynamical masses for the substellar companions Gl 229 B, Gl 758 B, HD 13724 B, HD 19467 B, HD 33632 Ab, and HD 72946 B. Our dynamical fits incorporate radial velocities, relative astrometry, and, most importantly, calibrated Hipparcos-Gaia EDR3 accelerations. For HD 33632 A and HD 72946 we perform three-body fits that account for their outer stellar companions. We present new relative astrometry of Gl 229 B with Keck/NIRC2, extending its observed baseline to 25 yr. We obtain a <1% mass measurement of 71.4 ± 0.6 M Jup for the first T dwarf Gl 229 B and a 1.2% mass measurement of its host star (0.579 ± 0.007 M ⊙) that agrees with the high-mass end of the M-dwarf mass–luminosity relation. We perform a homogeneous analysis of the host stars’ ages and use them, along with the companions’ measured masses and luminosities, to test substellar evolutionary models. Gl 229 B is the most discrepant, as models predict that an object this massive cannot cool to such a low luminosity within a Hubble time, implying that it may be an unresolved binary. The other companions are generally consistent with models, except for HD 13724 B, which has a host star activity age 3.8σ older than its substellar cooling age. Examining our results in context with other mass–age–luminosity benchmarks, we find no trend with spectral type but instead note that younger or lower-mass brown dwarfs are overluminous compared to models, while older or higher-mass brown dwarfs are underluminous. The presented mass measurements for some companions are so precise that the stellar host ages, not the masses, limit the analysis.
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Biller, B. A., A. Grandjean, S. Messina, S. Desidera, P. Delorme, A. M. Lagrange, F. J. Hambsch et al. "Dynamical masses for two M1 + mid-M dwarf binaries monitored during the SPHERE-SHINE survey". Astronomy & Astrophysics 658 (febbraio 2022): A145. http://dx.doi.org/10.1051/0004-6361/202142438.
Abstract (sommario):
We present orbital fits and dynamical masses for HIP 113201AB and HIP 36985AB, two M1 + mid-M dwarf binary systems monitored as part of the SPHERE-SHINE survey. To robustly determine the age of both systems via gyrochronology, we undertook a photometric monitoring campaign for HIP 113201 and GJ 282AB, the two wide K star companions to HIP 36985, using the 40 cm Remote Observatory Atacama Desert telescope. Based on this monitoring and gyrochronological relationships, we adopt ages of 1.2 ± 0.1 Gyr for HIP 113201AB and 750 ± 100 Myr for HIP 36985AB. These systems are sufficiently old that we expect that all components of these binaries have reached the main sequence. To derive dynamical masses for all components of the HIP 113201AB and HIP 36985AB systems, we used parallel-tempering Markov chain Monte Carlo sampling to fit a combination of radial velocity, direct imaging, and Gaia and HIPPARCOS astrometry. Fitting the direct imaging and radial velocity data for HIP 113201 yields a primary mass of 0.54 ± 0.03 M⊙, fully consistent with its M1 spectral type, and a secondary mass of 0.145 ± M⊙. The secondary masses derived with and without including HIPPARCOS-Gaia data are all considerably more massive than the 0.1 M⊙ mass estimated from the photometry of the companion. Thus, the dynamical impacts of this companion suggest that it is more massive than expected from its photometry. An undetected brown dwarf companion to HIP 113201B could be a natural explanation for this apparent discrepancy. At an age >1 Gyr, a 30 MJup companion to HIP 113201B would make a negligible (<1%) contribution to the system luminosity but could have strong dynamical impacts. Fitting the direct imaging, radial velocity, and HIPPARCOS-Gaia proper motion anomaly for HIP 36985AB, we find a primary mass of 0.54 ± 0.01 M⊙ and a secondary mass of 0.185 ± 0.001 M⊙, which agree well with photometric estimates of component masses, the masses estimated from MK– mass relationships for M dwarf stars, and previous dynamical masses in the literature.
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Bailer-Jones, C. A. L. "The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release". Astronomy & Astrophysics 609 (22 dicembre 2017): A8. http://dx.doi.org/10.1051/0004-6361/201731453.
Abstract (sommario):
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which pass within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars with large radial velocity uncertainties (>10 km s-1), and partly because of missing stars in GDR1 (especially at the bright end). The closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be 545 ± 59 Myr-1. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds to 87 ± 9 Myr-1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
38
Chen, Minghan, Yiting Li, Timothy D. Brandt, Trent J. Dupuy, Cátia V. Cardoso e Mark J. McCaughrean. "Precise Dynamical Masses of ε Indi Ba and Bb: Evidence of Slowed Cooling at the L/T Transition". Astronomical Journal 163, n. 6 (23 maggio 2022): 288. http://dx.doi.org/10.3847/1538-3881/ac66d2.
Abstract (sommario):
Abstract We report individual dynamical masses of 66.92 ± 0.36 M Jup and 53.25 ± 0.29 M Jup for the binary brown dwarfs ε Indi Ba and Bb, measured from long-term (≈10 yr) relative orbit monitoring and absolute astrometry monitoring data on the Very Large Telescope (VLT). Relative astrometry with NACO fully constrains the Keplerian orbit of the binary pair, while absolute astrometry with FORS2 measures the system’s parallax and mass ratio. We find a parallax consistent with the Hipparcos and Gaia values for ε Indi A, and a mass ratio for ε Indi Ba to Bb precise to better than 0.2%. ε Indi Ba and Bb have spectral types T1-1.5 and T6, respectively. With an age of 3.5 − 1.0 + 0.8 Gyr from ε Indi A’s activity, these brown dwarfs provide some of the most precise benchmarks for substellar cooling models. Assuming coevality, the very different luminosities of the two brown dwarfs and our moderate mass ratio imply a steep mass–luminosity relationship ( L ∝ M 5.37 ± 0.08 ) that can be explained by a slowed cooling rate in the L/T transition, as previously observed for other L/T binaries. Finally, we present a periodogram analysis of the near-infrared photometric data, but find no definitive evidence of periodic signals with a coherent phase.
39
Kervella, Pierre, Frédéric Arenou, François Mignard e Frédéric Thévenin. "Stellar and substellar companions of nearby stars from Gaia DR2". Astronomy & Astrophysics 623 (marzo 2019): A72. http://dx.doi.org/10.1051/0004-6361/201834371.
Abstract (sommario):
Context. The census of stellar and substellar companions of nearby stars is largely incomplete, in particular toward the low-mass brown dwarf and long-period exoplanets. It is, however, fundamentally important in the understanding of the stellar and planetary formation and evolution mechanisms. Nearby stars are particularly favorable targets for high precision astrometry. Aims. We aim to characterize the presence of physical companions of stellar and substellar mass in orbit around nearby stars. Methods. Orbiting secondary bodies influence the proper motion of their parent star through their gravitational reflex motion. Using the HIPPARCOS and Gaia’s second data release (GDR2) catalogs, we determined the long-term proper motion of the stars common to these two catalogs. We then searched for a proper motion anomaly (PMa) between the long-term proper motion vector and the GDR2 (or HIPPARCOS) measurements, indicative of the presence of a perturbing secondary object. We focussed our analysis on the 6741 nearby stars located within 50 pc, and we also present a catalog of the PMa for ≳99% of the HIPPARCOS catalog (≈117 000 stars). Results. 30% of the stars studied present a PMa greater than 3σ. The PMa allows us to detect orbiting companions, or set stringent limits on their presence. We present a few illustrations of the PMa analysis to interesting targets. We set upper limits of 0.1−0.3 MJ to potential planets orbiting Proxima between 1 and 10 au (Porb = 3 to 100 years). We confirm that Proxima is gravitationally bound to α Cen. We recover the masses of the known companions of ϵ Eri, ϵ Ind, Ross 614 and β Pic. We also detect the signature of a possible planet of a few Jovian masses orbiting τ Ceti. Conclusions. Based on only 22 months of data, the GDR2 has limitations. But its combination with the HIPPARCOS catalog results in very high accuracy PMa vectors, that already enable us to set valuable constraints on the binarity of nearby objects. The detection of tangential velocity anomalies at a median accuracy of σ(ΔvT) = 1.0 m s−1 per parsec of distance is already possible with the GDR2. This type of analysis opens the possibility to identify long period orbital companions otherwise inaccessible. For long orbital periods, Gaia’s complementarity to radial velocity and transit techniques (that are more sensitive to short orbital periods) already appears to be remarkably powerful.
40
Damljanovic, G., M. Stojanovic e J. Aleksic. "Independent analysis of γδ data of ILS and INDLS catalogs to obtain the spin of the bright Gaia DR2 reference frame". Serbian Astronomical Journal, n. 00 (2021): 2. http://dx.doi.org/10.2298/saj210428002d.
Abstract (sommario):
The Gaia DR2 reference frame should be without relative rotation to the quasars (QSOs) and consistent with the International Celestial Reference System (ICRS). For the faint part of DR2 (stars with Gaia magnitude G ? 16) that task was done via Gaia's observations of QSOs (G ? 17 mag), but the bright DR2 (G ? 13 mag) is difficult to validate and it rotates relative to the faint DR2 at rate of the order of 0.1 mas/yr. Very bright DR2 stars (G ? 6 mag) mostly have inferior astrometry. Here, the aim is to determine two spin components (?X and ?Y) of the bright DR2 using International Latitude Service (ILS, for 387 stars) and independent latitude stations (INDLS, for 682 stars) catalogs of proper motion in declination ??; both are referred to the Hipparcos reference frame and their stars are mostly from 4 to 8 mag in the V-band (critical part of DR2). Also, using the new Hipparcos (NHIP) values ?? for ILS and INDLS stars, we can see that the merit of the ILS and INDLS is the long time baseline (?t ? 90 years) important for ?? because the standard deviation of ?? is opposite to ?t. Applying the least squares method (LSM) to the differences of ?? between two catalogs (ILS-DR2, INDLS-DR2, etc.), our results support the mentioned spin. The 3? criterion and Tukey's fences method were used to reject some stars, the Abbe criterion to explain the variability in ILS-DR2 and other ?? differences, and the Shapiro-Wilk test to check the standard distribution of differences. The obtained ?Y is significant at the 2 ? level, and the ILS and INDLS catalogs could be useful for validation of the bright reference frame of Gaia DR2.
41
Franson, Kyle, e Brendan P. Bowler. "Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B". Astronomical Journal 165, n. 6 (22 maggio 2023): 246. http://dx.doi.org/10.3847/1538-3881/acca18.
Abstract (sommario):
Abstract Dynamical masses of giant planets and brown dwarfs are critical tools for empirically validating substellar evolutionary models and their underlying assumptions. We present a measurement of the dynamical mass and an updated orbit of PZ Tel B, a young brown dwarf companion orbiting a late-G member of the β Pic moving group. PZ Tel A exhibits an astrometric acceleration between Hipparcos and Gaia EDR3, which enables the direct determination of the companion’s mass. We have also acquired new Keck/NIRC2 adaptive optics imaging of the system, which increases the total baseline of relative astrometry to 15 yr. Our joint orbit fit yields a dynamical mass of 27 − 9 + 25 M Jup , semimajor axis of 27 − 4 + 14 au , eccentricity of 0.52 − 0.10 + 0.08 , and inclination of 91.73 − 0.32 + 0.36 ° . The companion’s mass is consistent within 1.1σ of predictions from four grids of hot-start evolutionary models. The joint orbit fit also indicates a more modest eccentricity of PZ Tel B than previous results. PZ Tel joins a small number of young (<200 Myr) systems with benchmark substellar companions that have dynamical masses and precise ages from moving group membership.
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Swimmer, Noah, Thayne Currie, Sarah Steiger, G. Mirek Brandt, Timothy D. Brandt, Olivier Guyon, Masayuki Kuzuhara et al. "SCExAO and Keck Direct Imaging Discovery of a Low-mass Companion Around the Accelerating F5 Star HIP 5319*". Astronomical Journal 164, n. 4 (21 settembre 2022): 152. http://dx.doi.org/10.3847/1538-3881/ac85a8.
Abstract (sommario):
Abstract We present the direct imaging discovery of a low-mass companion to the nearby accelerating F star, HIP 5319, using SCExAO coupled with the CHARIS, VAMPIRES, and MEC instruments in addition to Keck/NIRC2 imaging. CHARIS JHK (1.1–2.4 μm) spectroscopic data combined with VAMPIRES 750 nm, MEC Y, and NIRC2 L p photometry is best matched by an M3–M7 object with an effective temperature of T = 3200 K and surface gravity log(g) = 5.5. Using the relative astrometry for HIP 5319 B from CHARIS and NIRC2, and absolute astrometry for the primary from Gaia and Hipparcos, and adopting a log-normal prior assumption for the companion mass, we measure a dynamical mass for HIP 5319 B of 31 − 11 + 35 M J , a semimajor axis of 18.6 − 4.1 + 10 au, an inclination of 69.4 − 15 + 5.6 degrees, and an eccentricity of 0.42 − 0.29 + 0.39 . However, using an alternate prior for our dynamical model yields a much higher mass of 128 − 88 + 127 M J . Using data taken with the LCOGT NRES instrument we also show that the primary HIP 5319 A is a single star in contrast to previous characterizations of the system as a spectroscopic binary. This work underscores the importance of assumed priors in dynamical models for companions detected with imaging and astrometry, and the need to have an updated inventory of system measurements.
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Li, Yiting, Timothy D. Brandt, G. Mirek Brandt, Trent J. Dupuy, Daniel Michalik, Rebecca Jensen-Clem, Yunlin Zeng, Jacqueline Faherty e Elena L. Mitra. "Precise Masses and Orbits for Nine Radial-velocity Exoplanets". Astronomical Journal 162, n. 6 (26 novembre 2021): 266. http://dx.doi.org/10.3847/1538-3881/ac27ab.
Abstract (sommario):
Abstract Radial-velocity (RV) surveys have discovered hundreds of exoplanetary systems but suffer from a fundamental degeneracy between planet mass M p and orbital inclination i. In this paper, we resolve this degeneracy by combining RVs with complementary absolute astrometry taken from the Gaia EDR3 version of the cross calibrated Hipparcos–Gaia Catalog of Accelerations (HGCA). We use the Markov Chain Monte Carlo orbit code orvara to simultaneously fit literature RVs and absolute astrometry from the HGCA. We constrain the orbits, masses, and inclinations of nine single and massive RV companions orbiting nearby G and K stars. We confirm the planetary nature of six companions: HD 29021 b ( 4.47 − 0.65 + 0.67 M Jup ), HD 81040 b ( 7.24 − 0.37 + 1.0 M Jup ), HD 87883 b ( 6.31 − 0.32 + 0.31 M Jup ), HD 98649 b ( 9.7 − 1.9 + 2.3 M Jup ), HD 106252 b ( 10.00 − 0.73 + 0.78 M Jup ), and HD 171238 b ( 8.8 − 1.3 + 3.6 M Jup ). We place one companion, HD 196067 b ( 12.5 − 1.8 + 2.5 M Jup ) on the planet–brown dwarf boundary and two companions in the low-mass brown dwarf regime: HD 106515 Ab ( 18.9 − 1.4 + 1.5 M Jup ), and HD 221420 b ( 20.6 − 1.6 + 2.0 M Jup ). The brown dwarf HD 221420 b, with a semimajor axis of 9.99 − 0.70 + 0.74 au, a period of 27.7 − 2.5 + 3.0 yr, and an eccentricity of 0.162 − 0.030 + 0.035 represents a promising target for high-contrast imaging. The RV orbits of HD 87883 b, HD 98649 b, HD 171238 b, and HD 196067 b are not fully constrained yet because of insufficient RV data. We find two possible inclinations for each of these orbits due to difficulty in separating prograde from retrograde orbits, but we expect this will change decisively with future Gaia data releases.
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Currie, Thayne, G. Mirek Brandt, Timothy D. Brandt, Brianna Lacy, Adam Burrows, Olivier Guyon, Motohide Tamura et al. "Direct imaging and astrometric detection of a gas giant planet orbiting an accelerating star". Science 380, n. 6641 (14 aprile 2023): 198–203. http://dx.doi.org/10.1126/science.abo6192.
Abstract (sommario):
Direct imaging of gas giant exoplanets provides information on their atmospheres and the architectures of planetary systems. However, few planets have been detected in blind surveys with direct imaging. Using astrometry from the Gaia and Hipparcos spacecraft, we identified dynamical evidence for a gas giant planet around the nearby star HIP 99770. We confirmed the detection of this planet with direct imaging using the Subaru Coronagraphic Extreme Adaptive Optics instrument. The planet, HIP 99770 b, orbits 17 astronomical units from its host star, receiving an amount of light similar to that reaching Jupiter. Its dynamical mass is 13.9 to 16.1 Jupiter masses. The planet-to-star mass ratio [(7 to 8) × 10 −3 ] is similar to that of other directly imaged planets. The planet’s atmospheric spectrum indicates an older, less cloudy analog of the previously imaged exoplanets around HR 8799.
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de Bruijne, Jos, Hassan Siddiqui, Uwe Lammers, John Hoar, William O'Mullane e Timo Prusti. "Optimising the Gaia scanning law for relativity experiments". Proceedings of the International Astronomical Union 5, S261 (aprile 2009): 331–33. http://dx.doi.org/10.1017/s1743921309990597.
Abstract (sommario):
AbstractGaia is ESA's upcoming astrometry mission, building on the heritage of its predecessor, Hipparcos. The Gaia nominal scanning law (NSL) prescribes the ideal attitude of the spacecraft over the operational phase of the mission. As such, it precisely determines when certain areas of the sky are observed. From theoretical considerations on sky-sampling uniformity, it is easy to show that the optimum scanning law for a space astrometry experiment like Gaia is a revolving scan with uniform rotation around the instrument symmetry axis. Since thermal stability requirements for Gaia's payload require the solar aspect angle to be fixed, the optimum parallax resolving power is obtained by letting the spin axis precess around the solar direction. The precession speed has been selected as compromise, limiting the across-scan smearing of images when they transit the focal plane, providing sufficient overlap between successive “great-circle” scans of the fields of view, and guaranteeing overlap of successive precession loops. With this scanning law, with fixed solar-aspect angle, spin rate, and precession speed, only two free parameters remain: the initial spin phase and the initial precession angle, at the start of science operations. Both angles, and in particular the initial precession angle, can be initialized following various (programmatic) criteria. Examples are optimization/fine-tuning of the Earth-pointing angle, of the number and total duration of Galactic-plane scans, or of the ground-station scheduling. This paper explores various criteria, with particular emphasis on the opportunity to optimise the scanning-law initial conditions to “observe” the most favorable passages of bright stars very close to Jupiter's limb. This would allow a unique determination of the light deflection due to the quadrupole component of the gravitational field of this planet.
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Hernandez, X., R. A. M. Cortés, Christine Allen e R. Scarpa. "Challenging a Newtonian prediction through Gaia wide binaries". International Journal of Modern Physics D 28, n. 08 (giugno 2019): 1950101. http://dx.doi.org/10.1142/s0218271819501013.
Abstract (sommario):
Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modeled to include the effects of Galactic tides and stellar mass perturbers, over the lifetime of the solar neighborhood. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. Taking a carefully selected small sample of 81 solar neighborhood wide binaries from the Hipparcos catalog, we identify these same stars in the recent Gaia DR2, to test the prediction mentioned using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical [Formula: see text][Formula: see text]m.s[Formula: see text] value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.
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Feng, Fabo, Guillem Anglada-Escudé, Mikko Tuomi, Hugh R. A. Jones, Julio Chanamé, Paul R. Butler e Markus Janson. "Detection of the nearest Jupiter analogue in radial velocity and astrometry data". Monthly Notices of the Royal Astronomical Society 490, n. 4 (21 ottobre 2019): 5002–16. http://dx.doi.org/10.1093/mnras/stz2912.
Abstract (sommario):
ABSTRACT The presence of Jupiter is crucial to the architecture of the Solar system and models underline this to be a generic feature of planetary systems. We find the detection of the difference between the position and motion recorded by the contemporary astrometric satellite Gaia and its precursor Hipparcos can be used to discover Jupiter-like planets. We illustrate how observations of the nearby star ϵ Indi A giving astrometric and radial velocity data can be used to independently find the orbit of its suspected companion. The radial velocity and astrometric data provide complementary detections which allow for a much stronger solution than either technique would provide individually. We quantify ϵ Indi A b as the closest Jupiter-like exoplanet with a mass of 3 MJup on a slightly eccentric orbit with an orbital period of 45 yr. While other long-period exoplanets have been discovered, ϵ Indi A b provides a well-constrained mass and along with the well-studied brown dwarf binary in orbit around ϵ Indi A means that the system provides a benchmark case for our understanding of the formation of gas giant planets and brown dwarfs.
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Feng, Fabo, R. Paul Butler, Steven S. Vogt, Matthew S. Clement, C. G. Tinney, Kaiming Cui, Masataka Aizawa et al. "3D Selection of 167 Substellar Companions to Nearby Stars". Astrophysical Journal Supplement Series 262, n. 1 (26 agosto 2022): 21. http://dx.doi.org/10.3847/1538-4365/ac7e57.
Abstract (sommario):
Abstract We analyze 5108 AFGKM stars with at least five high-precision radial velocity points, as well as Gaia and Hipparcos astrometric data, utilizing a novel pipeline developed in previous work. We find 914 radial velocity signals with periods longer than 1000 days. Around these signals, 167 cold giants and 68 other types of companions are identified, through combined analyses of radial velocity, astrometry, and imaging data. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3%, and find a significant brown-dwarf valley around 40 M Jup. We also find a power-law distribution in the host binary fraction beyond 3 au, similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. Our work also reveals nine substellar systems (GJ 234 B, GJ 494 B, HD 13724 b, HD 182488 b, HD 39060 b and c, HD 4113 C, HD 42581 d, HD 7449 B, and HD 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. Depending on their ages, we estimate that an additional 10–57 substellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude.
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Franson, Kyle, Brendan P. Bowler, Timothy D. Brandt, Trent J. Dupuy, Quang H. Tran, G. Mirek Brandt, Yiting Li e Adam L. Kraus. "Dynamical Mass of the Young Substellar Companion HD 984 B". Astronomical Journal 163, n. 2 (7 gennaio 2022): 50. http://dx.doi.org/10.3847/1538-3881/ac35e8.
Abstract (sommario):
Abstract Model-independent masses of substellar companions are critical tools to validate models of planet and brown dwarf cooling, test their input physics, and determine the formation and evolution of these objects. In this work, we measure the dynamical mass and orbit of the young substellar companion HD 984 B. We obtained new high-contrast imaging of the HD 984 system with Keck/NIRC2 that expands the baseline of relative astrometry from 3 to 8 yr. We also present new radial velocities of the host star with the Habitable-Zone Planet Finder spectrograph at the Hobby-Eberly Telescope. Furthermore, HD 984 exhibits a significant proper motion difference between Hipparcos and Gaia EDR3. Our joint orbit fit of the relative astrometry, proper motions, and radial velocities yields a dynamical mass of 61 ± 4 M Jup for HD 984 B, placing the companion firmly in the brown dwarf regime. The new fit also reveals a higher eccentricity for the companion (e = 0.76 ± 0.05) compared to previous orbit fits. Given the broad age constraint for HD 984, this mass is consistent with predictions from evolutionary models. HD 984 B’s dynamical mass places it among a small but growing list of giant planet and brown dwarf companions with direct mass measurements.
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Zhang, Zhoujian, Brendan P. Bowler, Trent J. Dupuy, Timothy D. Brandt, G. Mirek Brandt, William D. Cochran, Michael Endl et al. "The McDonald Accelerating Stars Survey: Architecture of the Ancient Five-planet Host System Kepler-444". Astronomical Journal 165, n. 2 (27 gennaio 2023): 73. http://dx.doi.org/10.3847/1538-3881/aca88c.
Abstract (sommario):
Abstract We present the latest and most precise characterization of the architecture for the ancient (≈11 Gyr) Kepler-444 system, which is composed of a K0 primary star (Kepler-444 A) hosting five transiting planets and a tight M-type spectroscopic binary (Kepler-444 BC) with an A–BC projected separation of 66 au. We have measured the system’s relative astrometry using the adaptive optics imaging from Keck/NIRC2 and Kepler-444 A’s radial velocities from the Hobby-Eberly Telescope and reanalyzed relative radial velocities between BC and A from Keck/HIRES. We also include the Hipparcos-Gaia astrometric acceleration and all published astrometry and radial velocities in an updated orbit analysis of BC’s barycenter. These data greatly extend the time baseline of the monitoring and lead to significant updates to BC’s barycentric orbit compared to previous work, including a larger semimajor axis ( a = 52.2 − 2.7 + 3.3 au), a smaller eccentricity (e = 0.55 ± 0.05), and a more precise inclination ( i = 85 .° 4 − 0 .° 4 + 0 .° 3 ). We have also derived the first dynamical masses of B and C components. Our results suggest that Kepler-444 A’s protoplanetary disk was likely truncated by BC to a radius of ≈8 au, which resolves the previously noticed tension between Kepler-444 A’s disk mass and planet masses. Kepler-444 BC’s barycentric orbit is likely aligned with those of A’s five planets, which might be primordial or a consequence of dynamical evolution. The Kepler-444 system demonstrates that compact multiplanet systems residing in hierarchical stellar triples can form at early epochs of the universe and survive their secular evolution throughout cosmic time.