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Bundy, Kevin, David Law, Nick MacDonald, Kyle B. Westfall, T. Sivarani, Devika Divakar, Matthew Bershady et al. « The Stability of Fiber Spectrographs in the Faint-source Regime ». Astronomical Journal 164, no 3 (11 août 2022) : 94. http://dx.doi.org/10.3847/1538-3881/ac76cc.
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Abstract The use of optical fibers in astronomical instrumentation offers high-multiplex and light-gathering flexibility. However, with most previous fiber spectrographs optimized for large fields of view on modest-aperture telescopes, the performance of fibers in the context of faint targets on large telescopes remains largely untested. In this paper, we evaluate aspects of fiber stability, especially as they apply in the context of precision sky subtraction of faint sources at modest spectral resolution (R ∼ 3000). After introducing a framework for describing potential systematic errors, we use publicly available data from existing instruments, including instrumentation used by the fourth-generation Sloan Digital Sky Survey’s MaNGA project (MaNGA: Mapping Nearby Galaxies at Apache Point Observatory) and the Very Large Telescope’s FLAMES: Fiber Large Array Multi Element Spectrograph. We isolate sources of fiber systematics and estimate the observed amplitude of persistent residuals as well as stochastic noise contributions resulting from changing fiber stresses. Comparing these levels against their impact on various sky subtraction schemes demonstrates that 0.1% precision sky subtraction with fiber instruments is possible. As a demonstration, we show that the MaNGA instrument can deliver 0.2% residuals on bright near-IR sky lines with nonlocal sky subtraction, if pseudo-slit limitations are addressed by allocating 50% of its fibers to sky. We further highlight recently published deep exposures that achieved a 1σ background level of 27.6 AB per square arc second, equivalent to a precision of 0.2% of the sky background continuum.
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Iliev, Lubomir. « Recent Spectral Observations of Epsilon Aurigae in the Near-IR ». Proceedings of the International Astronomical Union 7, S282 (juillet 2011) : 95–96. http://dx.doi.org/10.1017/s1743921311027062.
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AbstractHigh resolution spectral observations of ϵ Aur were carried out in the near-IR spectral range. Observations were obtained with the Coudé-spectrograph of the 2m RCC telescope at National Astronomical Observatory Rozhen and cover all main phases of the current eclipse. Results revealed for the first time absorption components in O I and Ca II triplets and variations of N I lines. Estimation of the electron density was done using lines from the Paschen series of hydrogen.
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Origlia, L., et E. Oliva. « SIMPLE : A High Resolution Near IR Spectrograph for the European ELT ». Earth, Moon, and Planets 105, no 2-4 (8 juillet 2009) : 123–26. http://dx.doi.org/10.1007/s11038-009-9335-6.
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Ikeda, Yuji, Sohei Kondo, Shogo Otsubo, Satoshi Hamano, Chikako Yasui, Noriyuki Matsunaga, Hiroaki Sameshima et al. « Highly Sensitive, Non-cryogenic NIR High-resolution Spectrograph, WINERED ». Publications of the Astronomical Society of the Pacific 134, no 1031 (1 janvier 2022) : 015004. http://dx.doi.org/10.1088/1538-3873/ac1c5f.
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Abstract WINERED is a novel near-infrared (NIR) high-resolution spectrograph (HRS) that pursues the highest possible sensitivity to realize high-precision spectroscopy in the NIR as in the optical wavelength range. WINERED covers 0.9–1.35 μm (z, Y, and J-bands) with three modes (Wide mode and two Hires modes) at the maximum spectral resolutions of R = 28,000 and R = 70,000. For fulfilling the objective, WINERED is designed with an unprecedentedly high instrument throughput (up to 50% at maximum including the quantum efficiency of the array) that is three times or more than other existing optical/NIR HRSs. This is mainly realized by a combination of non-white pupil and no fiber-fed configuration in optical design, the moderate (optimized) wavelength coverage, and the high-throughput gratings. Another prominent feature of WINERED is “warm” instrument despite for infrared (IR) observations. Such non-cryogenic (no cold stop) IR instrument finally became possible with the combination of custom-made thermal-cut filter of 10−8 class, 1.7 μm cutoff HAWAII-2RG array, and a cold baffle reducing the direct thermal radiation to the IR array into the solid angle of f/2. The thermal background is suppressed below 0.1 photons pixel−1 s−1 even in the wide band of 0.9–1.35 μm under the environment of 290 K. WINERED had been installed to the 3.58 m New Technology Telescope at La Silla Observatory, ESO, since 2017. Even with the intermediate size telescope, WINERED was confirmed to provide a limiting magnitude (for SNR = 30 with 8 hr. integration time) of J = 16.4 mag for the Wide mode and J = 15.1 mag for the Hires mode, respectively, under the natural seeing conditions. These sensitivities are comparable to those for the existing NIR-HRSs attached to the 8–10 m class telescopes with AO. WINERED type spectrographs may become a critical not only for the currently on-going extremely large telescopes to reduce the developing cost and time but also for smaller telescopes to extend their lives with long programs.
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McGregor, Peter J., Peter Conroy, Gabe Bloxham et Jan van Harmelen. « Near-infrared Integral-Field Spectrograph (NIFS) : An Instrument Proposed for Gemini ». Publications of the Astronomical Society of Australia 16, no 3 (1999) : 273–87. http://dx.doi.org/10.1071/as99273.
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AbstractIn late 1998 the International Gemini Project Office identified a need for a low cost, near-infrared spectrograph to be commissioned on the Gemini South telescope on the shortest possible timescale. In response, the Research School of Astronomy and Astrophysics of the Australian National University proposed to design, construct, and commission a near-infrared, integral-field spectrograph on Gemini. The science drivers and novel design of the Near-infrared Integral-Field Spectrograph (NIFS) are described in this paper. NIFS will achieve significant economies in cost and schedule in several ways:• By addressing targeted science with high efficiency. NIFS will primarily target velocity measurements in galaxies to study the demographics of black holes in galactic nuclei and the evolution of structural properties in high redshift galaxies. However, NIFS will also be applied to a wide range of general astronomical topics, but these will not dictate the instrument design.• By adopting a largely fixed-format design. A 3·2″ × 3·2″ ‘stair-case’ integral field unit (IFU) will feed a near-infrared spectrograph with four fixed-angle gratings mounted on a single grating wheel. A single, fixed-format camera will form the spectral image on a 2048 × 2048 Rockwell HgCdTe HAWAII-2 array. Two-pixel spectral resolving powers of ∼5400 will be achieved with complete wavelength coverage in each of the J, H, and K photometric bands through 32 optimally sampled 0·1″ wide slitlets. The velocity resolution of ∼55 km s−1 will be sufficient to achieve the targeted science objectives, and will allow software rejection of OH airglow lines.• By packaging the NIFS instrument within a duplicate of the Near-Infrared Imager (NIRI) cryostat. The NIRI cryostat, On-Instrument Wavefront Sensor (OIWFS), detector focusing mechanism, control system, and EPICS software will all be duplicated with only minimal change. Construction of the duplicate NIRI cryostat, OIWFS, and control system will be done by the University of Hawaii.
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Ueta, Toshiya, David Fong et Margaret Meixner. « Westbrook's Molecular Gun : Discovery of Near-Infrared Microstructures and Molecular Bullets in AFGL 618 ». Symposium - International Astronomical Union 209 (2003) : 122. http://dx.doi.org/10.1017/s0074180900208279.
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We present high-sensitivity near-IR images of a carbon-rich proto-planetary nebula, AFGL 618, obtained with the Infrared Camera and Spectrograph (IRCS) mounted on the 8.2m Subaru Telescope. The deep near-IR images have revealed “bullets” and “horns” extending farther out from the edges of the previously known bipolar nebulosities that consist of dust-scattered star light component and shock-excited line emission component. That these bullets and horns represent the positions from which [Fe II] IR lines arise is strongly suggested from the spatial coincidence between these near-IR microstructures and the optical collimated outflow structure observed by the recent HST/WFPC2 imaging, together with the previous detection of shock-excited, forbidden IR lines of atomic species at those locations. At these positions of the near-IR mincrostructures, we have also discovered CO clumps moving at > 200 km s-1 from our re-analysis of the existing 12CO J = 1 – 0 data obtained with the Berkeley-Illinois-Maryland Association (BIMA) interferometer array. These findings indicate that fast-moving CO clumps seem to be impinging upon the surrounding ambient circumstellar shell, thereby causing shocked emission regions which manifest themselves as the near-IR microstructures at the shock interface. To deepen our understanding of the connection between the near-IR microstructures and the CO outflow structure, we are currently conducting higher resolution observation in CO lines with the BIMA array.
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Oliva, E., M. Rainer, A. Tozzi, N. Sanna, M. Iuzzolino et A. Brucalassi. « Experimental characterization of modal noise in multimode fibers for astronomical spectrometers ». Astronomy & ; Astrophysics 632 (21 novembre 2019) : A21. http://dx.doi.org/10.1051/0004-6361/201936610.
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Context. High resolution spectroscopy at high signal-to-noise ratios (S/Ns) is one the key techniques of the quantitative study of the atmospheres of extrasolar planets. Observations at near-infrared wavelengths with fiber-fed spectrographs coupled to extremely large telescopes are particularly important to tackle the ultimate goal of detecting biosignatures in rocky planets. Aims. To achieve high S/Ns in fiber-fed spectrogrpahs, the systematic noise effects introduced by the fibers must be properly understood and mitigated. In this paper we concentrate on the effects of modal noise in multimode fibers. Methods. Starting from our puzzling on-sky experience with the GIANO-TNG spectrometer we set up an infrared high resolution spectrometer in our laboratory and used this instrument to characterize the modal noise generated in fibers of different types (circular and octagonal) and sizes. Our experiment includes two conventional scrambling systems for fibers: a mechanical agitator and an optical double scrambler. Results. We find that the strength of the modal noise primarily depends on how the fiber is illuminated. It dramatically increases when the fiber is under-illuminated, either in the near field or in the far field. The modal noise is similar in circular and octagonal fibers. The Fourier spectrum of the noise decreases exponentially with frequency; i.e., the modal noise is not white but favors broad spectral features. Using the optical double scrambler has no effect on modal noise. The mechanical agitator has effects that vary between different types of fibers and input illuminations. In some cases this agitator has virtually no effect. In other cases, it mitigates the modal noise, but flattens the noise spectrum in Fourier space; i.e., the mechanical agitator preferentially filters the broad spectral features. Conclusions. Our results show that modal noise is frustratingly insensitive to the use of octagonal fibers and optical double scramblers; i.e., the conventional systems used to improve the performances of spectrographs fed via unevenly illuminated fibers. Fiber agitation may help in some cases, but its effect has to be verified on a case-by-case basis. More generally, our results indicate that the design of the fiber link feeding a spectrograph should be coupled with laboratory measurements that reproduce, as closely as possible, the conditions expected at the telescope.
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Siebenmorgen, R., P. Scicluna et J. Krełowski. « Far-infrared emission of massive stars ». Astronomy & ; Astrophysics 620 (23 novembre 2018) : A32. http://dx.doi.org/10.1051/0004-6361/201833546.
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We present results of the analysis of a sample of 22 stars of spectral types from O7 to B5 and luminosity classes I–V for which spectra from the Infrared Spectrograph (IRS) of Spitzer are available. The IRS spectra of these stars are examined for signs of excess infrared (IR) emission by comparison with stellar atmospheric spectra. We find that the spectra of half of the studied stars are dominated by excess emission in the far-IR, including all six super- and bright giants. In order to examine the origin of the far-IR excess, we supplement the Spitzer data with optical high-resolution echelle spectroscopy (λ∕Δλ ~ 105), near-IR high-contrast coronagraphic imaging taken with the SPHERE instrument at VLT with a spatial resolution of 0.′′05, and WISE and Herschel photometry. In the optical region, we detect various absorption and emission lines (H α, C III, and N III) irrespective of the far-IR excess. Pfund α and Humphrey α lines are observed at the same time as the far-IR excess. These lines are stronger in stars with far-IR excess than in stars without excess. A scattered-light disk in the central r ≲ 2.5′′ region of the far-IR excess stars HD 149404, HD 151804, and HD 154368 can be excluded from H band imaging down to a 1σ contrast of F(r)∕F∗~ 10−6. The far-IR excess is fit either by a free–free component from ionized gas as for the winds of hot stars or a large (1 pc) circumstellar dust shell. The putative dust envelopes required to explain the excess have a visual extinction as low as a few hundred μ-mag.
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Sarre, P. J., et T. R. Kendall. « Diffuse Interstellar Bands ». Symposium - International Astronomical Union 197 (2000) : 343–48. http://dx.doi.org/10.1017/s0074180900164927.
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The unidentified diffuse interstellar bands are observed in near-UV, visible and near-IR spectra recorded towards stars which are partially obscured by interstellar dust. Their origin is the longest standing problem in astronomical spectroscopy and dates back to the 1930s when systematic study of the bands first started. Proposals for the carriers range from molecular hydrogen to porphyrins and from colour centres to species adsorbed on grain surfaces. This paper contains a short review of the problem and a discussion of recent possible assignments of some of the bands to transitions of the H2, and molecules. Observations of ultra-high resolution spectra of diffuse absorption bands, optical diffuse emission bands from the Red Rectangle, and complementary studies of the 3.3 μm ‘unidentified’ infrared (UIR) emission band are described.
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Hamano, Satoshi, Naoto Kobayashi, Hideyo Kawakita, Keiichi Takenaka, Yuji Ikeda, Noriyuki Matsunaga, Sohei Kondo et al. « Survey of Near-infrared Diffuse Interstellar Bands in Y and J Bands. I. Newly Identified Bands ». Astrophysical Journal Supplement Series 262, no 1 (17 août 2022) : 2. http://dx.doi.org/10.3847/1538-4365/ac7567.
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Abstract We searched for diffuse interstellar bands (DIBs) in the 0.91 < λ < 1.33 μm region by analyzing the near-infrared (NIR) high-resolution (R = 20,000 and 28,000) spectra of 31 reddened early-type stars (0.04 < E(B − V) < 4.58) and an unreddened reference star. The spectra were collected using the WINERED spectrograph, which was mounted on the 1.3 m Araki telescope at Koyama Astronomical Observatory, Japan, in 2012–2016, and on the 3.58 m New Technology Telescope at La Silla Observatory, Chile, in 2017–2018. We detected 54 DIBs—25 of which are newly detected by this study—and eight DIB candidates. Using this updated list, the DIB distributions over a wide wavelength range, from optical to NIR, are investigated. The FWHM values of the NIR DIBs are found to be narrower than those of the optical DIBs, on average, which suggests that the DIBs at longer wavelengths tend to be caused by larger molecules. Assuming that the larger carriers are responsible for the DIBs at longer wavelengths, and have larger oscillator strengths, we found that the total column densities of the DIB carriers tend to decrease with increasing DIB wavelength. The candidate molecules and ions for the NIR DIBs are also discussed.
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Carmona, A., M. E. van den Ancker, Th Henning, Ya Pavlyuchenkov, C. P. Dullemond, M. Goto, D. Fedele et al. « Searching for H2 emission from protoplanetary disks using near- and mid-infrared high-resolution spectroscopy ». Proceedings of the International Astronomical Union 3, S249 (octobre 2007) : 359–68. http://dx.doi.org/10.1017/s1743921308016827.
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AbstractThe mass and dynamics of protoplanetary disks are dominated by molecular hydrogen (H2). However, observationally very little is known about the H2. In this paper, we discuss two projects aimed to constrain the properties of H2 in the disk's planet forming region (R<50AU). First, we present a sensitive survey for pure-rotational H2 emission at 12.278 and 17.035 μm in a sample of nearby Herbig Ae/Be and T Tauri stars using VISIR, ESO's VLT high-resolution mid-infrared spectrograph. Second, we report on a search for H2 ro-vibrational emission at 2.1228, 2.2233 and 2.2477 μm in the classical T Tauri star LkHα 264 and the debris disk 49 Cet employing CRIRES, ESO's VLT high-resolution near-infrared spectrograph.VISIR project: none of the sources show H2 mid-IR emission. The observed disks contain less than a few tenths of MJupiter of optically thin H2 at 150 K, and less than a few MEarth at T>300 K. % and higher T. Our non-detections are consistent with the low flux levels expected from the small amount of H2 gas in the surface layer of a Chiang and Goldreich (1997) Herbig Ae two-layer disk model. In our sources the H2 and dust in the surface layer have not significantly departed from thermal coupling (Tgas/Tdust<2) and the gas-to-dust ratio in the surface layer is very likely <1000.CRIRES project: The H2 lines at 2.1218 μm and 2.2233 μm are detected in LkHα 264. An upper limit on the 2.2477 μm H2 line flux in LkHα 264 is derived. 49 Cet does not exhibit H2 emission in any of observed lines. There are a few MMoon of optically thin hot H2 in the inner disk (∼0.1 AU) of LkHα 264, and less than a tenth of a MMoon of hot H2 in the inner disk of 49 Cet. The shape of the 1–0 S(0) line indicates that LkHα disk is close to face-on (i<35o). The measured 1–0 S(0)/1–0 S(1) and 2–1 S(1)/1–0 S(1) line ratios in LkHα 264 indicate that the H2 is thermally excited at T<1500 K. The lack of H2 emission in the NIR spectra of 49 Cet and the absence of Hα emission suggest that the gas in the inner disk of 49 Cet has dissipated.
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Matsuoka, K., Y. Toba, M. Shidatsu, Y. Ueda, K. Iwasawa, Y. Terashima, M. Imanishi, T. Nagao, A. Marconi et W. H. Wang. « Ratio of black hole to galaxy mass of an extremely red dust-obscured galaxy at z = 2.52 ». Astronomy & ; Astrophysics 620 (30 novembre 2018) : L3. http://dx.doi.org/10.1051/0004-6361/201833943.
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We present a near-infrared (NIR) spectrum of WISE J104222.11+164115.3, an extremely red dust-obscured galaxy (DOG), which has been observed with the Long-slit Intermediate Resolution Infrared Spectrograph (LIRIS) on the 4.2m William Hershel Telescope. This object was selected as a hyper-luminous DOG candidate at z ∼ 2 by combining the optical and IR photometric data based on the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE), although its redshift had not yet been confirmed. Based on the LIRIS observation, we confirmed its redshift of 2.521 and total IR luminosity of log(LIR/L⊙) = 14.57, which satisfies the criterion for an extremely luminous IR galaxy (ELIRG). Moreover, we indicate that this object seems to have an extremely massive black hole with MBH = 1010.92 M⊙ based on the broad Hα line: the host stellar mass is derived as M⋆ = 1013.55 M⊙ by a fit of the spectral energy distribution. Very recently, it has been reported that this object is an anomalous gravitationally lensed quasar based on near-IR high-resolution imaging data obtained with the Hubble Space Telescope. Its magnification factor has also been estimated with some uncertainty (i.e., μ = 53−122). We investigate the ratio of the black hole to galaxy mass, which is less strongly affected by a lensing magnification factor, instead of the absolute values of the luminosities and masses. We find that the MBH/M⋆ ratio (i.e., 0.0140–0.0204) is significantly higher than the local relation, following a sequence of unobscured quasars instead of obscured objects (e.g., submillimeter galaxies) at the same redshift. Moreover, the LIRIS spectrum shows strongly blueshifted oxygen lines with an outflowing velocity of ∼1100 km s−1, and our Swift X-ray observation also supports that this source is an absorbed AGN with an intrinsic column density of NHint = 4.9 × 1023 cm−2. These results imply that WISE J104222.11+164115.3 is in a blow-out phase at the end of the buried rapid black hole growth.
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Fuhrmeister, B., S. Czesla, L. Hildebrandt, E. Nagel, J. H. M. M. Schmitt, S. V. Jeffers, J. A. Caballero et al. « The CARMENES search for exoplanets around M dwarfs ». Astronomy & ; Astrophysics 640 (août 2020) : A52. http://dx.doi.org/10.1051/0004-6361/202038279.
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The He I infrared (IR) triplet at 10 830 Å is known as an activity indicator in solar-type stars and has become a primary diagnostic in exoplanetary transmission spectroscopy. He I IR lines are a tracer of the stellar extreme-ultraviolet irradiation from the transition region and corona. We study the variability of the He I triplet lines in a spectral time series of 319 M dwarf stars that was obtained with the CARMENES high-resolution optical and near-infrared spectrograph at Calar Alto. We detect He I IR line variability in 18% of our sample stars, all of which show Hα in emission. Therefore, we find detectable He I variability in 78% of the sub-sample of stars with Hα emission. Detectable variability is strongly concentrated in the latest spectral sub-types, where the He I lines during quiescence are typically weak. The fraction of stars with detectable He I variation remains lower than 10% for stars earlier than M3.0 V, while it exceeds 30% for the later spectral sub-types. Flares are accompanied by particularly pronounced line variations, including strongly broadened lines with red and blue asymmetries. However, we also find evidence for enhanced He I absorption, which is potentially associated with increased high-energy irradiation levels at flare onset. Generally, He I and Hα line variations tend to be correlated, with Hα being the most sensitive indicator in terms of pseudo-equivalent width variation. This makes the He I triplet a favourable target for planetary transmission spectroscopy.
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Fuhrmeister, B., S. Czesla, L. Hildebrandt, E. Nagel, J. H. M. M. Schmitt, D. Hintz, E. N. Johnson et al. « The CARMENES search for exoplanets around M dwarfs ». Astronomy & ; Astrophysics 632 (25 novembre 2019) : A24. http://dx.doi.org/10.1051/0004-6361/201936193.
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The He I infrared (IR) triplet at 10 830 Å is an important activity indicator for the Sun and in solar-type stars, however, it has rarely been studied in relation to M dwarfs to date. In this study, we use the time-averaged spectra of 319 single stars with spectral types ranging from M0.0 V to M9.0 V obtained with the CARMENES high resolution optical and near-infrared spectrograph at Calar Alto to study the properties of the He I IR triplet lines. In quiescence, we find the triplet in absorption with a decrease of the measured pseudo equivalent width (pEW) towards later sub-types. For stars later than M5.0 V, the He I triplet becomes undetectable in our study. This dependence on effective temperature may be related to a change in chromospheric conditions along the M dwarf sequence. When an emission in the triplet is observed, we attribute it to flaring. The absence of emission during quiescence is consistent with line formation by photo-ionisation and recombination, while flare emission may be caused by collisions within dense material. The He I triplet tends to increase in depth according to increasing activity levels, ultimately becoming filled in; however, we do not find a correlation between the pEW(He IR) and X-ray properties. This behaviour may be attributed to the absence of very inactive stars (LX∕Lbol < −5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in.
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Koss, Michael J., Ezequiel Treister, Darshan Kakkad, J. Andrew Casey-Clyde, Taiki Kawamuro, Jonathan Williams, Adi Foord et al. « UGC 4211 : A Confirmed Dual Active Galactic Nucleus in the Local Universe at 230 pc Nuclear Separation ». Astrophysical Journal Letters 942, no 1 (1 janvier 2023) : L24. http://dx.doi.org/10.3847/2041-8213/aca8f0.
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Abstract We present multiwavelength high-spatial resolution (∼0.″1, 70 pc) observations of UGC 4211 at z = 0.03474, a late-stage major galaxy merger at the closest nuclear separation yet found in near-IR imaging (0.″32, ∼230 pc projected separation). Using Hubble Space Telescope/Space Telescope Imaging Spectrograph, Very Large Telescope/MUSE+AO, Keck/OSIRIS+AO spectroscopy, and the Atacama Large Millimeter/submillimeter Array (ALMA) observations, we show that the spatial distribution, optical and near-infrared emission lines, and millimeter continuum emission are all consistent with both nuclei being powered by accreting supermassive black holes (SMBHs). Our data, combined with common black hole mass prescriptions, suggest that both SMBHs have similar masses, log M BH / M ⊙ ∼ 8.1 (south) and log M BH / M ⊙ ∼ 8.3 (north), respectively. The projected separation of 230 pc (∼6× the black hole sphere of influence) represents the closest-separation dual active galactic nuclei (AGN) studied to date with multiwavelength resolved spectroscopy and shows the potential of nuclear (<50 pc) continuum observations with ALMA to discover hidden growing SMBH pairs. While the exact occurrence rate of close-separation dual AGN is not yet known, it may be surprisingly high, given that UGC 4211 was found within a small, volume-limited sample of nearby hard X-ray detected AGN. Observations of dual SMBH binaries in the subkiloparsec regime at the final stages of dynamical friction provide important constraints for future gravitational wave observatories.
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Hocdé, V., N. Nardetto, S. Borgniet, E. Lagadec, P. Kervella, A. Mérand, N. Evans et al. « Pulsating chromosphere of classical Cepheids ». Astronomy & ; Astrophysics 641 (septembre 2020) : A74. http://dx.doi.org/10.1051/0004-6361/202037795.
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Context. It has recently been shown that the infrared (IR) emission of Cepheids, constant over the pulsation cycle, might be due to a pulsating shell of ionized gas with a radius of about 15% of that of the star radius, which could be attributed to the chromospheric activity of Cepheids. Aims. The aim of this paper is to investigate the dynamical structure of the chromosphere of Cepheids along the pulsation cycle and to quantify its size. Methods. We present Hα and calcium near-infrared triplet (Ca IR) profile variations using high-resolution spectroscopy with the UVES spectrograph of a sample of 24 Cepheids with a good period coverage from ≈3 to 60 days. After a qualitative analysis of the spectral line profiles, we quantified the Van Hoof effect (velocity gradient between the Hα and Ca IR) as a function of the period of the Cepheids. We then used the Schwarzschild mechanism (a line doubling due to a shock wave) to quantify the size of the chromosphere. Results. We find a significant Van Hoof effect for Cepheids with a period larger than P = 10 days. In particular, Hα lines are delayed with a velocity gradient up to Δv ≈ 30 km s−1 compared to Ca IR. By studying the shocks, we find that the size of the chromosphere of long-period Cepheids is of at least ≈50% of the stellar radius, which is consistent at first order with the size of the shell made of ionized gas previously found from the analysis of IR excess. Last, for most of the long-period Cepheids in the sample, we report a motionless absorption feature in the Hα line that we attribute to a circumstellar envelope that surrounds the chromosphere. Conclusions. Analyzing the Ca IR lines of Cepheids is of importance to potentially unbias the period–luminosity relation from their IR excess, particularly in the context of forthcoming observations of radial velocity measurements from the Radial Velocity Spectrometer on board Gaia, which could be sensitive to their chromosphere.
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Boccaletti, A., P. Thébault, N. Pawellek, A. M. Lagrange, R. Galicher, S. Desidera, J. Milli et al. « Two cold belts in the debris disk around the G-type star NZ Lupi ». Astronomy & ; Astrophysics 625 (mai 2019) : A21. http://dx.doi.org/10.1051/0004-6361/201935135.
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Context. Planetary systems hold the imprint of the formation and of the evolution of planets especially at young ages, and in particular at the stage when the gas has dissipated leaving mostly secondary dust grains. The dynamical perturbation of planets in the dust distribution can be revealed with high-contrast imaging in a variety of structures. Aims. SPHERE, the high-contrast imaging device installed at the VLT, was designed to search for young giant planets in long period, but is also able to resolve fine details of planetary systems at the scale of astronomical units in the scattered-light regime. As a young and nearby star, NZ Lup was observed in the course of the SPHERE survey. A debris disk had been formerly identified with HST/NICMOS. Methods. We observed this system in the near-infrared with the camera in narrow and broad band filters and with the integral field spectrograph. High contrasts are achieved by the mean of pupil tracking combined with angular differential imaging algorithms. Results. The high angular resolution provided by SPHERE allows us to reveal a new feature in the disk which is interpreted as a superimposition of two belts of planetesimals located at stellocentric distances of ~85 and ~115 au, and with a mutual inclination of about 5°. Despite the very high inclination of the disk with respect to the line of sight, we conclude that the presence of a gap, that is, a void in the dust distribution between the belts, is likely. Conclusions. We discuss the implication of the existence of two belts and their relative inclination with respect to the presence of planets.
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Mikolaitis, Š., A. Drazdauskas, R. Minkevičiūtė, E. Stonkutė, G. Tautvaišienė, L. Klebonas, V. Bagdonas, E. Pakštienė et R. Janulis. « High-resolution spectroscopic study of dwarf stars in the northern sky ». Astronomy & ; Astrophysics 628 (août 2019) : A49. http://dx.doi.org/10.1051/0004-6361/201835004.
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Context. New space missions, such as NASA TESS or ESA PLATO, will focus on bright stars, which have been largely ignored by modern large surveys, especially in the northern sky. Spectroscopic information is of paramount importance in characterising the stars and analysing planets possibly orbiting them, and in studying the Galactic disc evolution. Aims. The aim of this work was to analyse all bright (V < 8 mag) F, G, and K dwarf stars using high-resolution spectra in the selected sky fields near the northern celestial pole. Methods. The observations were carried out with the 1.65 m diameter telescope at the Molėtai Astronomical Observatory and a fibre-fed high-resolution spectrograph covering a full visible wavelength range (4000–8500 Å). The atmospheric parameters were derived using the classical equivalent width approach while the individual chemical element abundances were determined from spectral synthesis. For both tasks the one-dimensional plane-parallel LTE MARCS stellar model atmospheres were applied. The NLTE effects for the majority of elemental abundances in our sample were negligible; however, we did calculate the NLTE corrections for the potassium abundances, as they were determined from the large 7698.9 Å line. For manganese and copper we have accounted for a hyperfine splitting. Results. We determined the main atmospheric parameters, kinematic properties, orbital parameters, and stellar ages for 109 newly observed stars and chemical abundances of Na I, Mg I, Al I, Si I, Si II, S I, K I, Ca I, Ca II, Sc I, Sc II, Ti I, Ti II, V I, Cr I, Cr II, Mn I, Fe I, Fe II, Co I, Ni I, Cu I, and Zn I for 249 F, G, and K dwarf stars observed in the present study and in our previous study. The [Mg I/Fe I] ratio was adopted to define the thin-disc (α-poor) and thick-disc (α-rich) stars in our sample. We explored the behaviour of 21 chemical species in the [El/Fe I] versus [Fe I/H] and [El/Fe I] versus age planes, and compared the results with the latest Galactic chemical evolution models. We also explored [El/Fe I] gradients according to the mean Galactocentric distances and maximum height above the Galactic plane. Conclusions. We found that in the Galactic thin-disc [El/Fe I] ratios of α-elements and aluminium have a positive trend with respect to age while the trend of Mn is clearly negative. Abundances of other species do not display significant trends. While the current theoretical models are able to reproduce the generic trends of the elements, they often seem to overestimate or underestimate the observational abundances. We found that the α-element and zinc abundances have slightly positive or flat radial and vertical gradients, while gradients for the odd-Z element Na, K, V, and Mn abundances are negative.
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Valyavin, Gennady, Grigory Beskin, Azamat Valeev, Gazinur Galazutdinov, Sergei Fabrika, Iosif Romanyuk, Vitaly Aitov et al. « EXPLANATION : Exoplanet and Transient Event Investigation Project—Optical Facilities and Solutions ». Photonics 9, no 12 (8 décembre 2022) : 950. http://dx.doi.org/10.3390/photonics9120950.
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Over the past decades, the achievements in astronomical instrumentation have given rise to a number of novel advanced studies related to the analysis of large arrays of observational data. One of the most famous of these studies is a study of transient events in the near and far space and a search for exoplanets. The main requirements for such kinds of projects are a simultaneous coverage of the largest possible field of view with the highest possible detection limits and temporal resolution. In this study, we present a similar project aimed at creating an extensive, continuously updated survey of transient events and exoplanets. To date, the core of the project incorporates several 0.07–2.5 m optical telescopes and the 6-m BTA telescope of the Special Astrophysical Observatory of RAS (Russia), a number of other Russian observatories and the Bonhyunsan observatory of the Korea Astronomy and Space Science Institute (South Korea). Our attention is mainly focused on the description of two groups of small, wide-angle optical telescopes for primary detection. All the telescopes are originally designed for the goals of the project and may be of interest to the scientific community. A description is also given for a new, high-precision optical spectrograph for the Doppler studies of transient and exoplanet events detected within the project. We present here the philosophy, expectations and first results obtained during the first year of running the project.
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Hoeijmakers, H. J., J. V. Seidel, L. Pino, D. Kitzmann, J. P. Sindel, D. Ehrenreich, A. V. Oza et al. « Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) ». Astronomy & ; Astrophysics 641 (septembre 2020) : A123. http://dx.doi.org/10.1051/0004-6361/202038365.
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Context. WASP-121 b is a hot Jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere. Aims. We survey the transmission spectrum of WASP-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the Hubble Space Telescope (HST). Methods. We applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, TiO, VO, and SH in high-resolution transit spectra obtained with the HARPS spectrograph. We injected models assuming chemical and hydrostatic equilibrium with a varying temperature and composition to enable model comparison, and employed two bootstrap methods to test the robustness of our detections. Results. We detect neutral Mg, Na, Ca, Cr, Fe, Ni, and V, which we predict exists in equilibrium with a significant quantity of VO, supporting earlier observations by HST/WFC3. Non-detections of Ti and TiO support the hypothesis that Ti is depleted via a cold-trap mechanism, as has been proposed in the literature. Atomic line depths are under-predicted by hydrostatic models by a factor of 1.5 to 8, confirming recent findings that the atmosphere is extended. We predict the existence of significant concentrations of gas-phase TiO2, VO2, and TiS, which could be important absorbers at optical and near-IR wavelengths in hot Jupiter atmospheres. However, accurate line-list data are not currently available for them. We find no evidence for absorption by SH and find that inflated atomic lines can plausibly explain the slope of the transmission spectrum observed in the near-ultraviolet with HST. The Na I D lines are significantly broadened (FWHM ~50 to 70 km s−1) and show a difference in their respective depths of ~15 scale heights, which is not expected from isothermal hydrostatic theory. If this asymmetry is of astrophysical origin, it may indicate that Na I forms an optically thin envelope, reminiscent of the Na I cloud surrounding Jupiter, or that it is hydrodynamically outflowing.
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Aydi, E., K. L. Page, N. P. M. Kuin, M. J. Darnley, F. M. Walter, P. Mróz, D. A. H. Buckley et al. « Multiwavelength observations of nova SMCN 2016-10a – one of the brightest novae ever observed ». Monthly Notices of the Royal Astronomical Society 474, no 2 (14 octobre 2017) : 2679–705. http://dx.doi.org/10.1093/mnras/stx2678.
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Abstract We report on multiwavelength observations of nova Small Magellanic Cloud Nova 2016-10a. The present observational set is one of the most comprehensive for any nova in the Small Magellanic Cloud, including low-, medium-, and high-resolution optical spectroscopy and spectropolarimetry from Southern African Large Telescope, Folded Low-Order Yte-Pupil Double-Dispersed Spectrograph, and Southern Astrophysical Research; long-term Optical Gravitational Lensing Experiment V- and I-bands photometry dating back to 6 yr before eruption; Small and Moderate Aperture Research Telescope System optical and near-IR photometry from ∼11 d until over 280 d post-eruption; Swift satellite X-ray and ultraviolet observations from ∼6 d until 319 d post-eruption. The progenitor system contains a bright disc and a main sequence or a sub-giant secondary. The nova is very fast with t2 ≃ 4.0 ± 1.0 d and t3 ≃ 7.8 ± 2.0 d in the V band. If the nova is in the SMC, at a distance of ∼61 ± 10 kpc, we derive MV, max ≃ −10.5 ± 0.5, making it the brightest nova ever discovered in the SMC and one of the brightest on record. At day 5 post-eruption the spectral lines show a He/N spectroscopic class and an Full Width at Half Maximum of ∼3500 km s−1, indicating moderately high ejection velocities. The nova entered the nebular phase ∼20 d post-eruption, predicting the imminent super-soft source turn-on in the X-rays, which started ∼28 d post-eruption. The super-soft source properties indicate a white dwarf mass between 1.2 and 1.3 M⊙ in good agreement with the optical conclusions.
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Abe, Lyu, Nicolas Epchtein, Wolfgang Ansorge, Stefania Argentini, Ian Bryson, Marcel Carbillet, Gavin Dalton et al. « A European vision for a “Polar Large Telescope” project ». Proceedings of the International Astronomical Union 8, S288 (août 2012) : 243–50. http://dx.doi.org/10.1017/s174392131201695x.
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AbstractThe Polar Large Telescope (PLT) project is primarily aimed at undertaking large, wide band synoptic astronomical surveys in the infrared in order to provide critical data to the forthcoming generation of observational facilities such as ALMA, JWST, LSST and the E–ELT, and to complement the observations obtained with them. Sensitive thermal IR surveys beyond 2.3 μm cannot be carried out from any existing ground based observatory and the Antarctic Plateau is the only place on the ground where it can be envisaged, thanks to its unique atmospheric and environmental properties, such as the turbulence profile (image quality), the low opacity and the reduced thermal background emission of the sky. These unique conditions enable high angular resolution wide field surveys in the near thermal infrared (2.3–5 μm). This spectral range is particularly well suited to tackling key astrophysical questions such as: i) investigating the nature of the distant universe, the first generation of stars and the latest stages of stellar evolution, ii) understanding transient phenomena such as gamma ray-bursts and Type Ia supernovae, iii) increasing our knowledge of extra-solar planets. Further instruments may broaden the expected science outcomes of such a 2–4 m class telescope especially for the characterization of galaxies at very large distance to provide new clues in the mysteries of dark matter and energy. Efforts will be made to merge this project with other comparable projects within an international consortium.
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Tautvaišienė, G., C. Viscasillas Vázquez, Š. Mikolaitis, E. Stonkutė, R. Minkevičiūtė, A. Drazdauskas et V. Bagdonas. « Abundances of neutron-capture elements in thin- and thick-disc stars in the solar neighbourhood ». Astronomy & ; Astrophysics 649 (mai 2021) : A126. http://dx.doi.org/10.1051/0004-6361/202039979.
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Aims. The aim of this work is to determine abundances of neutron-capture elements for thin- and thick-disc F, G, and K stars in several selected sky fields near the north ecliptic pole and to compare the results with the Galactic chemical evolution models, to explore elemental gradients according to stellar ages, mean galactocentric distances, and maximum heights above the Galactic plane. Methods. The observational data were obtained with the 1.65 m telescope at the Molėtai Astronomical Observatory and a fibre-fed high-resolution spectrograph covering a full visible wavelength range (4000−8500 Å). Elemental abundances were determined using a differential line-by-line spectrum synthesis using the TURBOSPECTRUM code with the MARCS stellar model atmospheres and accounting for the hyperfine-structure effects. Results. We determined abundances of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu for 424 thin- and 82 thick-disc stars. The sample of thick-disc stars shows a clearly visible decrease in [Eu/Mg] with increasing metallicity compared to the thin-disc stars, bringing more evidence of a different chemical evolution in these two Galactic components. Abundance correlation with age slopes for the investigated thin-disc stars are slightly negative for the majority of s-process dominated elements, while r-process dominated elements have positive correlations. Our sample of thin-disc stars with ages spanning from 0.1 to 9 Gyr gives the [Y/Mg] = 0.022 (±0.015)−0.027 (±0.003)⋅age [Gyr] relation. However, for the thick-disc stars, when we also took data from other studies into account, we found that [Y/Mg] cannot serve as an age indicator. The radial abundance-to-iron gradients in the thin disc are negligible for the s-process dominated elements and become positive for the r-process dominated elements. The vertical gradients are negative for the light s-process dominated elements and become positive for the r-process dominated elements. In the thick disc, the radial abundance-to-iron slopes are negligible, and the vertical slopes are predominantly negative.
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De Cat, Peter, Jan Cuypers, Ronny Blomme, Yves Frémat, Martin Groenewegen, Patricia Lampens, Alex Lobel, Thierry Pauwels, Griet Van de Steene et Peter van Hoof. « The BINA collaboration : science at the Royal Observatory of Belgium ». Bulletin de la Société Royale des Sciences de Liège, 2018, 92–101. http://dx.doi.org/10.25518/0037-9565.7528.
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The Belgo-Indian Network for Astronomy and Astrophysics (BINA) is a collaboration between Indian and Belgian astronomical institutes with the main aim to optimize the scientific output of the Indo-Belgian telescopes, being the 4.0-m International Liquid Mirror Telescope and the 3.6-m Devasthal Optical Telescope. These new facilities are both located at the Devasthal Observatory near Nainital, India. In this contribution, we introduce projects that are of scientific interest for colleagues of the department “Astronomy and Astrophysics” of the Royal Observatory of Belgium (ROB). It serves as an invitation for Indian astronomers to participate. We highlight how these projects could benefit from observations with the Indo-Belgian telescopes by using instruments from the first-generation (currently offered) and/or the next-generation (development or design phase). We show that, from an ROB point-of-view, the BINA would be the most successful if the 3.6-m DOT would be equipped with an efficient optical high-resolution spectrograph.
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« Commission 9 : Instruments and techniques ». Transactions of the International Astronomical Union 23, no 1 (1997) : 498–514. http://dx.doi.org/10.1017/s0251107x00011779.
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During the period covered by this report, major progresses have been achieved in various fields of astronomical techniques and instruments. The era of large telescopes has been opened with the commissioning of the 2 Keck telescopes and the final construction phase for major facilities (ESO, JNLT, LBT, Gemini, etc). More than ten telescopes, with aperture larger than 8m, will be ready to scrutinize the sky, at the beginning of the next century. A Spanish project (GRANTBCAN) remains incompletely financed at this time. The power of these telescopes will be maximum when full diffraction limit capabilities will be available at their focus. The period 1994-1997 has seen major and spectacular achievements with realisation of several operationnal adaptative optic systems on 4m-class telescopes (ESO, CFHT). Diffraction limits have been reached at near-IR wavelength and partial correction, even in the visible, are bringing resolution comparable to space observations. All 8-10m projects require adaptative optics and have plans for it. In the meantime, 3-4m class telescopes are beeing equiped as well, so that AO will appear everywhere within the next 3 years. The necessary complement of adaptive optics, ie: the laser guide star, is thoroughly studied in order to provide full coverage for atmospheric compensation all over the sky. Projects of monochromatic and polychromatic laser stars are flourishing in relation with all telescopes with aperture of 3m-plus adaptative optics projects. Field coverage and achievable resolution require good pixel sampling and therefore large format detectors. Projects of very large format cameras for the visible and infrared are considered, up to 16kxl6k (MEGACAM at CFHT for 1.5 degrees field). Progress has been obtained in the industry to reduce gaps in between bootable CCDs, to reduce amplifiers noise and improve sensitivity. High angular resolution capabilities will gain another magnitude when the actual developments on interferometry with small telescopes will be tranfered to arrays of large telescopes (ESO, Keck, etc). Resolutions of 0.001 arc. sec will be available within 5 years leading to a gain of a factor 1000 compared to a 3.5m telescope operating today without adaptive optics.