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Piatti, Andrés E. "Globular Cluster Candidates in the Sagittarius Dwarf Galaxy". Astronomical Journal 162, nr 6 (24.11.2021): 261. http://dx.doi.org/10.3847/1538-3881/ac2833.
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Abstract Recently, new Sagittarius (Sgr) dwarf-galaxy globular clusters were discovered, which opens the question of the actual size of the Sgr globular cluster population, and therefore on our understanding of the Sgr galaxy formation and accretion history of the Milky Way. Based on Gaia EDR3 and SDSS IV DR16 (APOGEE-2) data sets, we performed an analysis of the color–magnitude diagrams (CMDs) of the eight new Sgr globular clusters found by Minniti et al. from a sound cleaning of the contamination of Milky Way and Sgr field stars, complemented by available kinematic and metal abundance information. The cleaned CMDs and spatial stellar distibutions reveal the presence of stars with a wide range of cluster membership probabilities. Minni 332 turned out to be a younger (<9 Gyr) and more metal-rich ([M/H] ≳ −1.0 dex) globular cluster than M54, the nuclear Sgr globular cluster; as could also be the case of Minni 342, 348, and 349, although their results are less convincing. Minni 341 could be an open cluster candidate (age < 1 Gyr, [M/H] ∼ −0.3 dex), while the analyses of Minni 335, 343, and 344 did not allow us to confirm their physical reality. We also built the Sgr cluster frequency (CF) using available ages of the Sgr globular clusters and compared it with that obtained from the Sgr star formation history. Both CFs are in excellent agreement. However, the addition of eight new globular clusters with ages and metallicities distributed according to the Sgr age–metallicity relationship turns out in a remarkably different CF.
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Lardo, C., M. Bellazzini, E. Pancino, E. Carretta, A. Bragaglia i E. Dalessandro. "Mining SDSS in search of multiple populations in globular clusters". Astronomy & Astrophysics 525 (6.12.2010): A114. http://dx.doi.org/10.1051/0004-6361/201015662.
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Vanderbeke, Joachim, Michael J. West, Roberto De Propris, Eric W. Peng, John P. Blakeslee, Andrés Jordán, Patrick Côté i in. "G2C2 – I. Homogeneous photometry for Galactic globular clusters in SDSS passbands". Monthly Notices of the Royal Astronomical Society 437, nr 2 (16.11.2013): 1725–33. http://dx.doi.org/10.1093/mnras/stt2002.
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Morrison, Heather L., Zhibo Ma, James L. Clem, Deokkeun An, Thomas Connor, Andrew Schechtman-Rook, Luca Casagrande i in. "GLOBULAR AND OPEN CLUSTERS OBSERVED BY SDSS/SEGUE: THE GIANT STARS". Astronomical Journal 151, nr 1 (18.12.2015): 7. http://dx.doi.org/10.3847/0004-6256/151/1/7.
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Vanderbeke, Joachim, Roberto De Propris, Sven De Rijcke, Maarten Baes, Michael J. West i John P. Blakeslee. "G2C2 – III. Structural parameters for Galactic globular clusters in SDSS passbands". Monthly Notices of the Royal Astronomical Society 450, nr 3 (maj 2015): 2692–707. http://dx.doi.org/10.1093/mnras/stv850.
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Fernández-Trincado, José G., Dante Minniti, Timothy C. Beers, Sandro Villanova, Doug Geisler, Stefano O. Souza, Leigh C. Smith i in. "The enigmatic globular cluster UKS 1 obscured by the bulge: H-band discovery of nitrogen-enhanced stars". Astronomy & Astrophysics 643 (listopad 2020): A145. http://dx.doi.org/10.1051/0004-6361/202039328.
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The presence of nitrogen-enriched stars in globular clusters provides key evidence for multiple stellar populations (MPs), as has been demonstrated with globular cluster spectroscopic data towards the bulge, disk, and halo. In this work, we employ the VVV Infrared Astrometric Catalogue (VIRAC) and the DR16 SDSS-IV release of the APOGEE survey to provide the first detailed spectroscopic study of the bulge globular cluster UKS 1. Based on these data, a sample of six selected cluster members was studied. We find the mean metallicity of UKS 1 to be [Fe/H] = −0.98 ± 0.11, considerably more metal-poor than previously reported, and a negligible metallicity scatter, typical of that observed by APOGEE in other Galactic globular clusters. In addition, we find a mean radial velocity of 66.1 ± 12.9 km s−1, which is in good agreement with literature values, within 1σ. By selecting stars in the VIRAC catalogue towards UKS 1, we also measure a mean proper motion of (μαcos(δ), μδ) = (−2.77 ± 0.23, −2.43 ± 0.16) mas yr−1. We find strong evidence for the presence of MPs in UKS 1, since four out of the six giants analysed in this work have strong enrichment in nitrogen ([N/Fe] ≳ +0.95) accompanied by lower carbon abundances ([C/Fe] ≲ −0.2). Overall, the light- (C, N), α- (O, Mg, Si, Ca, Ti), Fe-peak (Fe, Ni), Odd-Z (Al, K), and the s-process (Ce, Nd, Yb) elemental abundances of our member candidates are consistent with those observed in globular clusters at similar metallicity. Furthermore, the overall star-to-star abundance scatter of elements exhibiting the multiple-population phenomenon in UKS 1 is typical of that found in other global clusters (GCs), and larger than the typical errors of some [X/Fe] abundances. Results from statistical isochrone fits in the VVV colour-magnitude diagrams indicate an age of 13.10−1.29+0.93 Gyr, suggesting that UKS 1 is a fossil relic in the Galactic bulge.
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Szigeti, László, Szabolcs Mészáros, Gyula M. Szabó, José G. Fernández-Trincado, Richard R. Lane i Roger E. Cohen. "The rotation of selected globular clusters and the differential rotation of M3 in multiple populations from the SDSS-IV APOGEE-2 survey". Monthly Notices of the Royal Astronomical Society 504, nr 1 (12.04.2021): 1144–51. http://dx.doi.org/10.1093/mnras/stab1007.
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ABSTRACT In this paper, we analyse 10 globular clusters in order to measure their rotational properties by using high precision radial velocity data from the SDSS-IV APOGEE-2 survey. Out of the 10 clusters we were able to successfully measure the rotation speed and position angle of the rotation axis for 9 clusters (M2, M3, M5, M12, M13, M15, M53, M92, M107). The comparison between our results and previous ones shows a really good agreement within our uncertainties. For four of the globular clusters, M3, M13, M5, and M15, we separated the sample into two generation of stars using their [Al/Fe] abundances and examined the kinematic features of these generations separately from one another. In case of M3, we found significant difference between the rotational properties of first and second populations, confirming for the first time the predictions of several numerical simulations from the literature. The other three clusters (M5, M13, M15) also show smaller deviation between the two groups of stars, but those deviations are comparable to our errors.
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Vanderbeke, Joachim, Michael J. West, Roberto De Propris, Eric W. Peng, John P. Blakeslee, Andrés Jordán, Patrick Côté i in. "G2C2 – II. Integrated colour–metallicity relations for Galactic globular clusters in SDSS passbands". Monthly Notices of the Royal Astronomical Society 437, nr 2 (16.11.2013): 1734–49. http://dx.doi.org/10.1093/mnras/stt2012.
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Mészáros, Szabolcs, Thomas Masseron, D. A. García-Hernández, Carlos Allende Prieto, Timothy C. Beers, Dmitry Bizyaev, Drew Chojnowski i in. "Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code – II. The Southern clusters and overview". Monthly Notices of the Royal Astronomical Society 492, nr 2 (16.12.2019): 1641–70. http://dx.doi.org/10.1093/mnras/stz3496.
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ABSTRACT We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce, and Nd abundances of 2283 red giant stars in 31 globular clusters from high-resolution spectra observed in both the Northern and Southern hemisphere by the SDSS-IV APOGEE-2 survey. This unprecedented homogeneous data set, largest to date, allows us to discuss the intrinsic Fe spread, the shape, and statistics of Al-Mg and N-C anti-correlations as a function of cluster mass, luminosity, age, and metallicity for all 31 clusters. We find that the Fe spread does not depend on these parameters within our uncertainties including cluster metallicity, contradicting earlier observations. We do not confirm the metallicity variations previously observed in M22 and NGC 1851. Some clusters show a bimodal Al distribution, while others exhibit a continuous distribution as has been previously reported in the literature. We confirm more than two populations in ω Cen and NGC 6752, and find new ones in M79. We discuss the scatter of Al by implementing a correction to the standard chemical evolution of Al in the Milky Way. After correction, its dependence on cluster mass is increased suggesting that the extent of Al enrichment as a function of mass was suppressed before the correction. We observe a turnover in the Mg-Al anticorrelation at very low Mg in ω Cen, similar to the pattern previously reported in M15 and M92. ω Cen may also have a weak K-Mg anticorrelation, and if confirmed, it would be only the third cluster known to show such a pattern.
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Horta, Danny, Ricardo P. Schiavon, J. Ted Mackereth, Timothy C. Beers, José G. Fernández-Trincado, Peter M. Frinchaboy, D. A. García-Hernández i in. "The chemical compositions of accreted and in situ galactic globular clusters according to SDSS/APOGEE". Monthly Notices of the Royal Astronomical Society 493, nr 3 (18.02.2020): 3363–78. http://dx.doi.org/10.1093/mnras/staa478.
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ABSTRACT Studies of the kinematics and chemical compositions of Galactic globular clusters (GCs) enable the reconstruction of the history of star formation, chemical evolution, and mass assembly of the Galaxy. Using the latest data release (DR16) of the SDSS/APOGEE survey, we identify 3090 stars associated with 46 GCs. Using a previously defined kinematic association, we break the sample down into eight separate groups and examine how the kinematics-based classification maps into chemical composition space, considering only α (mostly Si and Mg) elements and Fe. Our results show that (i) the loci of both in situ and accreted subgroups in chemical space match those of their field counterparts; (ii) GCs from different individual accreted subgroups occupy the same locus in chemical space. This could either mean that they share a similar origin or that they are associated with distinct satellites which underwent similar chemical enrichment histories; (iii) the chemical compositions of the GCs associated with the low orbital energy subgroup defined by Massari and collaborators is broadly consistent with an in situ origin. However, at the low-metallicity end, the distinction between accreted and in situ populations is blurred; (iv) regarding the status of GCs whose origin is ambiguous, we conclude the following: the position in Si–Fe plane suggests an in situ origin for Liller 1 and a likely accreted origin for NGC 5904 and NGC 6388. The case of NGC 288 is unclear, as its orbital properties suggest an accretion origin, its chemical composition suggests it may have formed in situ.
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Wang, Song, Jun Ma i Jifeng Liu. "Globular clusters in the outer halo of M 31". Astronomy & Astrophysics 623 (marzec 2019): A65. http://dx.doi.org/10.1051/0004-6361/201834748.
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In this paper, we present photometry of 53 globular clusters (GCs) in the M 31 outer halo, including the GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV), SDSS ugriz, 15 intermediate-band filters of BATC, and 2MASS JHKs bands. By comparing the multicolour photometry with stellar population synthesis models, we determine the metallicities, ages, and masses for these GCs, aiming to probe the merging/accretion history of M 31. We find no clear trend of metallicity and mass with the de-projected radius. The halo GCs younger than ∼8 Gyr are mostly located at the de-projected radii around 100 kpc, but this may be due to a selection effect. We also find that the halo GCs have consistent metallicities with their spatially associated substructures, which provides further evidence of the physical association between them. Both the disc and halo GCs in M 31 show a bimodal luminosity distribution. However, we should emphasise that there are more faint halo GCs which are not seen in the disc. The bimodal luminosity function of the halo GCs may reflect a different origin or evolution environment in their original hosts. The M 31 halo GCs include one intermediate metallicity group (−1.5 < [Fe/H] < −0.4) and one metal-poor group ([Fe/H] < −1.5), while the disc GCs have one metal-rich group more. There are considerable differences between the halo GCs in M 31 and the Milky Way (MW). The total number of GCs in M 31 is approximately three times greater than in the MW, however M 31 has about six times more halo GCs than the MW. Compared to the halo GCs of M 31, those of the MW are mostly metal-poor. Both the numerous halo GCs and the higher-metallicity component are suggestive of an active merger history of M 31.
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Gontcharov, George A., Maxim Yu Khovritchev i Aleksandr V. Mosenkov. "Isochrone fitting of Galactic globular clusters – II. NGC 6205 (M13)". Monthly Notices of the Royal Astronomical Society 497, nr 3 (18.08.2020): 3674–93. http://dx.doi.org/10.1093/mnras/staa1694.
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ABSTRACT We present new isochrone fits to colour–magnitude diagrams of the Galactic globular cluster NGC 6205 (M13). We utilize 34 photometric bands from the ultraviolet to mid-infrared by use of data from the HST, Gaia DR2, SDSS, unWISE, Pan-STARRS DR1, and other photometric sources. In our isochrone fitting we use the PARSEC, MIST, DSEP, BaSTI, and IAC-BaSTI theoretical models and isochrones, both for the solar-scaled and He–α-enhanced abundances, with a metallicity of about [Fe/H] = −1.58 adopted from the literature. The colour–magnitude diagrams, obtained with pairs of filters from different datasets but of similar effective wavelengths, show some colour offsets up to 0.04 mag between the fiducial sequences and isochrones. We attribute these offsets to systematic differences of the datasets. Some intrinsic systematic differences of the models/isochrones remain in our results: the derived distances and ages are different for the ultraviolet, optical and infrared photometry used, while the derived ages are different for the different models/isochrones, e.g. in the optical range from 12.3 ± 0.7 Gyr for He–α-enhanced DSEP to 14.4 ± 0.7 Gyr for MIST. Despite the presence of multiple stellar populations, we obtain convergent estimates for the dominant population: best-fitting distance 7.4 ± 0.2 kpc, true distance modulus 14.35 ± 0.06 mag, parallax 0.135 ± 0.004 mas, extinction AV = 0.12 ± 0.02, and reddening E(B − V) = 0.04 ± 0.01. These estimates agree with other recent estimates; however, the extinction and reddening are twice as high as generally accepted. The derived empirical extinction law agrees with the Cardelli–Clayton–Mathis extinction law with the best-fitting $R_\mathrm{V}=3.1^{+1.6}_{-1.1}$.
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Masseron, T., D. A. García-Hernández, Sz Mészáros, O. Zamora, F. Dell’Agli, C. Allende Prieto, B. Edvardsson i in. "Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code". Astronomy & Astrophysics 622 (luty 2019): A191. http://dx.doi.org/10.1051/0004-6361/201834550.
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Aims. We seek to provide abundances of a large set of light and neutron-capture elements homogeneously analyzed that cover a wide range of metallicity to constrain globular cluster (GC) formation and evolution models. Methods. We analyzed a large sample of 885 GCs giants from the SDSS IV-Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We used the Cannon results to separate the red giant branch and asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then used the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) to derive metallicity, microturbulence, macroturbulence, many light-element abundances, and the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data. Results. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for low-metallicity GC stars. Furthermore, while we confirm most of the known correlations and anticorrelation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement. At the same time, these stars show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anticorrelation of the Al spread against clusters metallicity and luminosity, but the data do not allow us to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters. Conclusions. Large and homogeneously analyzed samples from ongoing spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anticorrelation, thus yielding new constrains for GCs formation/evolution models.
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Barbosa, Fabrícia O., Rafael M. Santucci, Silvia Rossi, Guilherme Limberg, Angeles Pérez-Villegas i Hélio D. Perottoni. "The SDSS-Gaia View of the Color–Magnitude Relation for Blue Horizontal-branch Stars". Astrophysical Journal 940, nr 1 (1.11.2022): 30. http://dx.doi.org/10.3847/1538-4357/ac983f.
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Abstract We present an updated sample of blue horizontal-branch (BHB) stars selected from the photometric and spectroscopic data from Sloan Digital Sky Survey and its associated project Sloan Extension for Galactic Understanding and Exploration (SEGUE). With these data, we selected candidates for A-type stars in the color–color space and then a mixture modeling technique was implemented in order to distinguish between BHB and main-sequence/blue-straggler stars based on their surface gravity values ( log g ) estimated by the SEGUE Stellar Parameter Pipeline. Our robust approach allows us to attribute individual probabilities of each star truly being in the BHB stage. Hence, our method is advantageous in comparison to previous SEGUE BHB selections that adopted simple log g cuts. We also revisit the color–magnitude relation for these stars and propose two calibrations, based on updated distances for Galactic globular clusters, to estimate absolute magnitudes with (g − r)0 and (u − r)0 colors.
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Koo, Jae-Rim, Young Sun Lee, Hye-Jin Park, Young Kwang Kim i Timothy C. Beers. "Determination of Sodium Abundance Ratio from Low-resolution Stellar Spectra and Its Applications". Astrophysical Journal 925, nr 1 (1.01.2022): 35. http://dx.doi.org/10.3847/1538-4357/ac3423.
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Abstract We present a method to determine sodium abundance ratios ([Na/Fe]) using the Na i D doublet lines in low-resolution (R ∼ 2000) stellar spectra. As stellar Na i D lines are blended with those produced by the interstellar medium, we developed a technique for removing the interstellar Na i D lines using the relationship between extinction, which is proportional to E(B − V), and the equivalent width of the interstellar Na i D absorption lines. When measuring [Na/Fe], we also considered corrections for nonlocal thermodynamic equilibrium (NLTE) effects. Comparisons with data from high-resolution spectroscopic surveys suggest that the expected precision of [Na/Fe] from low-resolution spectra is better than 0.3 dex for stars with [Fe/H] > −3.0. We also present a simple application employing the estimated [Na/Fe] values for a large number of stellar spectra from the Sloan Digital Sky Survey (SDSS). After classifying the SDSS stars into Na-normal, Na-high, and Na-extreme, we explore their relation to stars in Galactic globular clusters (GCs). We find that while the Na-high SDSS stars exhibit a similar metallicity distribution function (MDF) to that of the GCs, indicating that the majority of such stars may have originated from GC debris, the MDF of the Na-normal SDSS stars follows that of typical disk and halo stars. As there is a high fraction of carbon-enhanced metal-poor stars among the Na-extreme stars, they may have a non-GC origin, perhaps due to mass-transfer events from evolved binary companions.
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Koch, Andreas, Eva K. Grebel i Sarah L. Martell. "Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo buildup with SDSS-IV". Astronomy & Astrophysics 625 (maj 2019): A75. http://dx.doi.org/10.1051/0004-6361/201834825.
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There is ample evidence in the Milky Way for globular cluster (GC) disruption. It may therefore be expected that part of the Galactic halo field star population may also once have formed in GCs. We seek to quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed “second-generation stars”. These are stars showing light-element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands. Based on this indicator, past studies have placed the fraction of halo stars with a GC origin between a few to up to 50%. Using low-resolution spectra from the most recent data release (DR14) of the latest extension of the Sloan Digital Sky Survey (SDSS-IV), we were able to identify 118 metal-poor (−1.8 ≤ [Fe/H] ≤ −1.3) CN-strong stars in a sample of 4470 halo giant stars out to ∼50 kpc. This increases the number of known halo stars with GC-like light-element abundances by a factor of two and results in an observed fraction of these stars of 2.6 ± 0.2%. Using an updated formalism to account for the fraction of stars lost early on in the GC evolution, we thus estimate the fraction of the Galactic halo that stems from disrupted clusters to be very low, at 11 ± 1%. This number would represent the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit. Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs, the ratio of first-to-second generation stars, and other GC parameters. We carefully tested the influence of varying these parameters on the final result and find that under realistic scenarios, this fraction depends on the main assumptions at less than 10 percentage points. We further recover a flat trend in this fraction with Galactocentric radius, with a marginal indication of a rise beyond 30 kpc that could reflect the ex situ origin of the outer halo as is also seen in other stellar tracers.
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Mészáros, Szabolcs, Thomas Masseron, José G. Fernández-Trincado, D. A. García-Hernández, László Szigeti, Katia Cunha, Matthew Shetrone i in. "Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code – III. ω Cen". Monthly Notices of the Royal Astronomical Society 505, nr 2 (28.04.2021): 1645–60. http://dx.doi.org/10.1093/mnras/stab1208.
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ABSTRACT We study the multiple populations of ω Cen by using the abundances of Fe, C, N, O, Mg, Al, Si, K, Ca, and Ce from the high-resolution, high signal-to-noise (S/N > 70) spectra of 982 red giant stars observed by the SDSS-IV/APOGEE-2 survey. We find that the shape of the Al–Mg and N–C anticorrelations changes as a function of metallicity, continuous for the metal-poor groups, but bimodal (or unimodal) at high metallicities. There are four Fe populations, similarly to previous literature findings, but we find seven populations based on Fe, Al, and Mg abundances. The evolution of Al in ω Cen is compared to its evolution in the Milky Way and in five representative globular clusters. We find that the distribution of Al in metal-rich stars of ω Cen closely follows what is observed in the Galaxy. Other α-elements and C, N, O, and Ce are also compared to the Milky Way, and significantly elevated abundances are observed over what is found in the thick disc for almost all elements. However, we also find some stars with high metallicity and low [Al/Fe], suggesting that ω Cen could be the remnant core of a dwarf galaxy, but the existence of these peculiar stars needs an independent confirmation. We also confirm the increase in the sum of CNO as a function of metallicity previously reported in the literature and find that the [C/N] ratio appears to show opposite correlations between Al-poor and Al-rich stars as a function of metallicity.
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Rich, R. Michael, Christian I. Johnson, Michael Young, Iulia T. Simion, William I. Clarkson, Catherine Pilachowski, Scott Michael i in. "The Blanco DECam bulge survey. I. The survey description and early results". Monthly Notices of the Royal Astronomical Society 499, nr 2 (18.08.2020): 2340–56. http://dx.doi.org/10.1093/mnras/staa2426.
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ABSTRACT The Blanco Dark Energy Camera (DECam) Bulge survey is a Vera Rubin Observatory (LSST) pathfinder imaging survey, spanning ∼200 deg2 of the Southern Galactic bulge, −2° < b < −13° and −11° < l < +11°. We have employed the CTIO-4 m telescope and the DECam to image a contiguous ∼200 deg2 region of the relatively less reddened Southern Galactic bulge, in SDSS u + Pan-STARRSgrizy. Optical photometry with its large colour baseline will be used to investigate the age and metallicity distributions of the major structures of the bulge. Included in the survey footprint are 26 globular clusters imaged in all passbands. Over much of the bulge, we have Gaia DR2 matching astrometry to i ∼ 18, deep enough to reach the faint end of the red clump. This paper provides the background, scientific case, and description of the survey. We present an array of new reddening-corrected colour–magnitude diagrams that span the extent of Southern Galactic bulge. We argue that a population of massive stars in the blue loop evolutionary phase, proposed to lie in the bulge, are instead at ∼2 kpc from the Sun and likely red clump giants in the old disc. A bright red clump near (l, b) = (+ 8°, −4°) may be a feature in the foreground disc, or related to the long bar reported in earlier work. We also report the first map of the blue horizontal branch population spanning the Blanco DECam Bulge Survey field of regard, and our data do not confirm the reality of a number of proposed globular clusters in the bulge.
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Hawkins, Keith, Adrian M. Price-Whelan, Allyson A. Sheffield, Aidan Z. Subrahimovic, Rachael L. Beaton, Vasily Belokurov, Denis Erkal i in. "On the Hunt for the Origins of the Orphan–Chenab Stream: Detailed Element Abundances with APOGEE and Gaia". Astrophysical Journal 948, nr 2 (1.05.2023): 123. http://dx.doi.org/10.3847/1538-4357/acb698.
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Abstract Stellar streams in the Galactic halo are useful probes of the assembly of galaxies like the Milky Way. Many tidal stellar streams that have been found in recent years are accompanied by a known progenitor globular cluster or dwarf galaxy. However, the Orphan–Chenab (OC) stream is one case where a relatively narrow stream of stars has been found without a known progenitor. In an effort to find the parent of the OC stream, we use astrometry from the early third data release of ESA’s Gaia mission (Gaia EDR3) and radial velocity information from the Sloan Digital Sky Survey (SDSS)-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to find up to 13 stars that are likely members of the OC stream. We use the APOGEE survey to study the chemical nature (for up to 10 stars) of the OC stream in the α (O, Mg, Ca, Si, Ti, and S), odd-Z (Al, K, and V), Fe-peak (Fe, Ni, Mn, Co, and Cr), and neutron-capture (Ce) elemental groups. We find that the stars that make up the OC stream are not consistent with a monometallic population and have a median metallicity of −1.92 dex with a dispersion of 0.28 dex. Our results also indicate that the α elements are depleted compared to the known Milky Way populations and that its [Mg/Al] abundance ratio is not consistent with second-generation stars from globular clusters. The detailed chemical pattern of these stars, namely the [α/Fe]–[Fe/H] plane and the metallicity distribution, indicates that the OC stream progenitor is very likely to be a dwarf spheroidal galaxy with a mass of ∼106 M ⊙.
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Mamon, G. A., J. Chevalier, A. J. Romanowsky i R. Wojtak. "Dark matter inner slope and concentration in galaxies: from the Fornax dwarf to M87". Proceedings of the International Astronomical Union 10, S311 (lipiec 2014): 16–19. http://dx.doi.org/10.1017/s1743921315003312.
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AbstractWe apply two new state-of-the-art methods that model the distribution of observed tracers in projected phase space to lift the mass / velocity anisotropy (VA) degeneracy and deduce constraints on the mass profiles of galaxies, as well as their VA. We first show how a distribution function based method applied to the satellite kinematics of otherwise isolated SDSS galaxies shows convincing observational evidence of age matching: red galaxies have more concentrated dark matter (DM) halos than blue galaxies of the same stellar or halo mass. Then, applying the MAMPOSSt technique to M87 (traced by its red and blue globular clusters) we find that very cuspy DM is favored, unless we release priors on DM concentration or stellar mass (leading to unconstrained slope). For the Fornax dwarf spheroidal (traced by its metal-rich and metal-poor stars), the inner DM slope is unconstrained, with weak evidence for a core if the stellar mass is fixed. This highlights how priors are crucial for DM modeling. Finally, we find that blue GCs around M87 and metal-rich stars in Fornax have tangential outer VA.
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Hanke, Michael, Andreas Koch, Zdeněk Prudil, Eva K. Grebel i Ulrich Bastian. "Purveyors of fine halos". Astronomy & Astrophysics 637 (maj 2020): A98. http://dx.doi.org/10.1051/0004-6361/202037853.
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A long-lasting open question in the field of Galactic archeology refers to the size of the contribution from former globular cluster (GC) stars to the formation of the stellar halo of the Milky Way. We contribute to answering this important question by establishing observational links between the present-day halo field star population and GCs. To this end, we combined astrometric information such as space motions and parallaxes from the second data release of the Gaia mission (Gaia DR2) with spectroscopic radial velocities and metallicities ([Fe/H]) from the Sloan Digital Sky Survey (SDSS-IV, DR14) to end up with a seven-dimensional chemodynamical information space for more than 3 × 105 stars. Moreover, from our previous study, we incorporated the sample of halo giant stars with a distinct chemical signature (strong CN bandheads) that resembles the light-elements anomaly otherwise only seen in the second generation of globular cluster stellar populations. Using three different tagging techniques – among which is the exploration of conservative integrals of motion – we are able to establish unique associations between 151 extratidal stars in the neighborhood of eight GCs, which coincide with earlier findings of stellar envelopes beyond the tidal radius and even beyond (out to several tens of tidal radii). In addition, we trace the possible origin of about 62% of the sample of CN-strong giants to their potential host clusters. We find a connection between several of the involved GCs and the Gaia-Enceladus and Sequoia merger events. By establishing kinematic and chemical connections between 17 CN-strong stars and their surrounding fields, we identify co-moving groups of stars at the same [Fe/H] with a possible cluster origin. Some of these associations contain RR Lyrae variables, which allows meaningful distance inferences to be made. From these, we find strong evidence that four CN-strong stars and their associates are connected to the Sagittarius stream whilst their tightly confined [Fe/H] may hint to a birth site in M 54, the massive cluster in Sagittarius’ core remnant. Finally, by employing the counts of CN-strong and bona-fide CN-normal giants from our novel sample, we provide tentative estimates for the fraction of first-generation cluster stars among all stars lost to the halo. In the immediate cluster vicinity, this value amounts to 50.0 ± 16.7% while the associations in the halo field rather imply 80.2−5.2+4.9%. We speculate that – if proven real by spectroscopic follow-up – the disparity between these numbers could indicate a major contribution of low-mass clusters to the overall number of stars escaped to the halo or could alternatively suggest strong mass loss from the first generation during early cluster dissolution.
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Maraston, C., L. Hill, D. Thomas, R. Yan, Y. Chen, J. Lian, T. Parikh i in. "Stellar population models based on the SDSS-IV MaStar library of stellar spectra – I. Intermediate-age/old models". Monthly Notices of the Royal Astronomical Society 496, nr 3 (2.06.2020): 2962–97. http://dx.doi.org/10.1093/mnras/staa1489.
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ABSTRACT We use the first release of the SDSS/MaStar stellar library comprising ∼9000, high S/N spectra, to calculate integrated spectra of stellar population models. The models extend over the wavelength range 0.36–1.03 µm and share the same spectral resolution ($R\sim 1800$) and flux calibration as the SDSS-IV/MaNGA galaxy data. The parameter space covered by the stellar spectra collected thus far allows the calculation of models with ages and chemical composition in the range $\rm {\mathit{ t}\gt 200 \,Myr, -2 \lt = [Z/H] \lt = + 0.35}$, which will be extended as MaStar proceeds. Notably, the models include spectra for dwarf main-sequence stars close to the core H-burning limit, as well as spectra for cold, metal-rich giants. Both stellar types are crucial for modelling λ > 0.7 µm absorption spectra. Moreover, a better parameter coverage at low metallicity allows the calculation of models as young as 500 Myr and the full account of the blue horizontal branch phase of old populations. We present models adopting two independent sets of stellar parameters (Teff, log g, [Z/H]). In a novel approach, their reliability is tested ‘on the fly’ using the stellar population models themselves. We perform tests with Milky Way and Magellanic Clouds globular clusters, finding that the new models recover their ages and metallicities remarkably well, with systematics as low as a few per cent for homogeneous calibration sets. We also fit a MaNGA galaxy spectrum, finding residuals of the order of a few per cent comparable to the state-of-art models, but now over a wider wavelength range.
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Liu, X. W., H. B. Yuan, Z. Y. Huo, L. C. Deng, J. L. Hou, Y. H. Zhao, G. Zhao i in. "LSS-GAC – A LAMOST Spectroscopic Survey of the Galactic Anti-center". Proceedings of the International Astronomical Union 9, S298 (maj 2013): 310–21. http://dx.doi.org/10.1017/s1743921313006510.
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AbstractAs a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) will survey a significant volume of the Galactic thin/thick disks and halo in a contiguous sky area of ~3,400 sq.deg., centered on the Galactic anti-center (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3800–9000 low resolution (R ~1,800) spectra for a statistically complete sample of ≳ 3 M stars of all colors, uniformly and randomly selected from (r, g - r) and (r, r - i) Hess diagrams obtained from a CCD imaging photometric survey of ~5,400 sq.deg. with the Xuyi 1.04/1.20 m Schmidt Telescope, ranging from r = 14.0 to a limiting magnitude of r = 17.8 (18.5 for limited fields). The survey will deliver spectral classification, radial velocity (Vr) and stellar parameters (effective temperature (Teff), surface gravity (log g) and metallicity [Fe/H]) for millions of Galactic stars. Together with Gaia which will provide accurate distances and tangential velocities for a billion stars, the LSS-GAC will yield a unique data set to study the stellar populations, chemical composition, kinematics and structure of the disks and their interface with the halo, identify streams of debris of tidally disrupted dwarf galaxies and clusters, probe the gravitational potential and dark matter distribution, map the 3D distribution of interstellar dust extinction, search for rare objects (e.g. extremely metal-poor or hyper-velocity stars), and ultimately advance our understanding of the assemblage of the Milky Way and other galaxies and the origin of regularity and diversity of their properties.The survey was initiated in the fall of 2012 and expected to complete in the spring of 2017. Hitherto, about 0.4 M spectra of S/N(λ7450) ≥ 10 per pixel have been accumulated. In addition, bright nights have been used to target stars brighter than 14 mag and have so far generated over 0.4 M spectra, yielding an excellent sample of local stars to probe the solar neighborhood. LSP3, a set of pipelines tailored to the need of LSS-GAC, for spectral flux-calibration, and radial velocity and stellar parameter determinations, have been developed at Peking University, based on packages developed for the SDSS and those at the National Astronomical Observatories of Chinese Academy of Sciences. Comparisons of multi-epoch observations, with the SDSS results, as well as applying the pipelines to open and globular clusters show that LSP3 has achieved a precision of 5 km s−1, 110 K, 0.15 dex and 0.15 dex for Vr, Teff, log g and [Fe/H], respectively. The data are publicly available, subject to regulations of the LAMOST data policy, and begin to yield scientific results. The potential of LSS-GAC and power of existing data are illustrated with examples of selected problems.
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Fernández-Trincado, José G., Ronald Mennickent, Mauricio Cabezas, Olga Zamora, Sarah L. Martell, Timothy C. Beers, Vinicius M. Placco i in. "Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB star". Astronomy & Astrophysics 631 (29.10.2019): A97. http://dx.doi.org/10.1051/0004-6361/201935369.
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We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = −1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance reanalysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code. We manually re-derive the main element families, namely light elements (C, N), elements (O, Mg, Si), the iron-peak element (Fe), s-process element (Ce), and light odd-Z element (Al). Our analysis confirms the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of +0.69, and shows that the abundances of C and Al are slightly discrepant from those of a typical mildly metal-poor red giant branch star, but exhibit Mg, Si, O and s-process abundances (Ce) of typical field stars. We also detect a particularly large variability in the radial velocity of this star over the period of the APOGEE-2 observations; the most likely orbit fit to the radial velocity data has a period of 730.89 ± 106.86 days, a velocity semi-amplitude of 9.92 ± 0.14 km s−1, and an eccentricity of ∼0.1276 ± 0.1174. These data support the hypothesis of a binary companion, which has probably been polluted by a now-extinct asymptotic giant branch star.
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Li, Qing-Zheng, Yang Huang, Xiao-Bo Dong, Hua-Wei Zhang, Timothy C. Beers i Zhen Yuan. "On the Origins of Extreme Velocity Stars as Revealed by Large-scale Galactic Surveys". Astronomical Journal 166, nr 1 (12.06.2023): 12. http://dx.doi.org/10.3847/1538-3881/acd1dc.
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Abstract We assemble a large sample of 12,784 high-velocity stars with total velocity V GSR ≥ 300 km s−1, selected from RAVE DR5, SDSS DR12, LAMOST DR8, APOGEE DR16, GALAH DR2, and Gaia EDR3. In this sample, 52 are marginally hypervelocity star (HVS) candidates that have V GSR exceeding their local escape velocities within 2σ confidence levels, 40 of which are discovered for the first time. All of the candidates are metal-poor, late-type halo stars, which are significantly different from the previously identified HVSs, which are largely massive early-type stars, discovered by extreme radial velocity. This finding suggests that our newly identified HVS candidates are ejected by different mechanisms from the previous population. To investigate their origins, for 547 extreme velocity stars with V GSR ≥ 0.8V esc, we reconstruct their backward-integrated trajectories in the Galactic potential. According to the orbital analysis, no candidates are found to be definitely ejected from the Galactic-center (GC), while eight metal-poor extreme velocity stars are found to have a closest distance to the GC within 1 kpc. Intriguingly, 15 extreme velocity stars (including 2 HVS candidates) are found to have experienced close encounters with the Sagittarius dSph, suggesting that they originated from this dSph. This hypothesis is supported by an analysis of the [α/Fe]–[Fe/H] diagram. From a preliminary analysis of all of the 547 extreme velocity stars, we propose a general picture–star ejection from Galactic subsystems such as dwarf galaxies and globular clusters can be an important channel to produce extreme velocity stars or even HVSs, particularly the metal-poor late-type halo population.
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Bandyopadhyay, Avrajit, Sivarani Thirupathi, Timothy C. Beers i A. Susmitha. "A high-resolution spectroscopic study of two new Na- and Al-rich field giants–likely globular cluster escapees in the Galactic halo". Monthly Notices of the Royal Astronomical Society 494, nr 1 (13.03.2020): 36–43. http://dx.doi.org/10.1093/mnras/staa671.
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ABSTRACT The stars SDSS J0646+4116 and SDSS J1937+5024 are relatively bright stars that were initially observed as a part of the SDSS/MARVELS pre-survey. They were selected, on the basis of their weak CH G bands, along with a total of 60 others, in the range of halo globular cluster (GC) metallicities for high-resolution spectroscopic follow-up as a part of the HESP-GOMPA survey (Hanle Echelle SPectrograph – Galactic survey Of Metal Poor stArs). The stars exhibit typical nucleosynthesis signatures expected from the so-called second-generation stars of GCs. The light-element anticorrelation of Mg–Al is detected, along with elevated abundances of Na. Carbon is found to be depleted, which is compatible with expectation. Lithium is also detected in SDSS J0646+4116 and SDSS J1937+5024; the measured abundances are similar to those of normal halo giant stars. These bright escapees provide a unique opportunity to study the nucleosynthesis events of GC in great detail, and shed light on their chemical-enrichment histories.
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Jahandar, Farbod, Kim A. Venn, Matthew D. Shetrone, Mike Irwin, Jo Bovy, Charli M. Sakari, Collin L. Kielty, Ruth A. R. Digby i Peter M. Frinchaboy. "The peculiar globular cluster Palomar 1 and persistence in the SDSS-APOGEE data base". Monthly Notices of the Royal Astronomical Society 470, nr 4 (23.06.2017): 4782–93. http://dx.doi.org/10.1093/mnras/stx1592.
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Fernández-Trincado, J. G., O. Zamora, Diogo Souto, R. E. Cohen, F. Dell’Agli, D. A. García-Hernández, T. Masseron i in. "H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia". Astronomy & Astrophysics 627 (lipiec 2019): A178. http://dx.doi.org/10.1051/0004-6361/201834391.
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We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea that NGC 6522 stars are formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary polluters of intra-cluster medium. The peculiar abundance signatures of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.
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Martell, Sarah L., Matthew D. Shetrone, Sara Lucatello, Ricardo P. Schiavon, Szabolcs Mészáros, Carlos Allende Prieto, D. A. García Hernández, Timothy C. Beers i David L. Nidever. "CHEMICAL TAGGING IN THE SDSS-III/APOGEE SURVEY: NEW IDENTIFICATIONS OF HALO STARS WITH GLOBULAR CLUSTER ORIGINS". Astrophysical Journal 825, nr 2 (13.07.2016): 146. http://dx.doi.org/10.3847/0004-637x/825/2/146.
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Fritz, Tobias K., Sean T. Linden, Paul Zivick, Nitya Kallivayalil i Jo Bovy. "Using ground based data as a precursor for Gaia in getting proper motions of satellites". Proceedings of the International Astronomical Union 12, S330 (kwiecień 2017): 210–13. http://dx.doi.org/10.1017/s1743921317005750.
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AbstractWe present our effort to measure the proper motions of satellites in the halo of the Milky Way with mainly ground based telescopes as a precursor on what is possible with Gaia. For our first study, we used wide field optical data from the LBT combined with a first epoch of SDSS observations, on the globular cluster Palomar 5 (Pal 5). Since Pal 5 is associated with a tidal stream it is very useful to constrain the shape of the potential of the Milky Way. The motion and other properties of the Pal 5 system constrain the inner halo of the Milky Way to be rather spherical. Further, we combined adaptive optics and HST to get an absolute proper motion of the globular cluster Pyxis. Using the proper motion and the line-of-sight velocity we find that the orbit of Pyxis is rather eccentric with its apocenter at more than 100 kpc and its pericenter at about 30 kpc. The dynamics excludes an association with the ATLAS stream, the Magellanic clouds, and all satellites of the Milky Way at least down to the mass of Leo II. However, the properties of Pyxis, like metallicity and age, point to an origin from a dwarf of at least the mass of Leo II. We therefore propose that Pyxis originated from an unknown relatively massive dwarf galaxy, which is likely today fully disrupted. Assuming that Pyxis is bound to the Milky Way we derive a 68% lower limit on the mass of the Milky Way of 9.5 × 1011 M⊙.
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Santiago, Basílio, i Brian Yanny. "The Dark Energy Survey: perspectives for resolved stellar population studies". Proceedings of the International Astronomical Union 5, S262 (sierpień 2009): 265–69. http://dx.doi.org/10.1017/s1743921310002899.
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AbstractThe Dark Energy Survey (DES) will cover 5000 sq. deg. in grizY filters. Although its main goals are related to cosmology, it will yield photometric measurements of over 108 stars, most of them belonging to the Galaxy. DES will increase the sampling depth of very low-luminosity stellar and sub-stellar species, such as white, red, and brown dwarfs, by a factor of several as compared to SDSS. The structure of the Galactic halo, including its complex sub-structures caused by accretion remnants and globular cluster tidal tails, will also be probed and analyzed. DES will also allow comparison of star counts between Northern and Southern Galactic hemispheres to unprecedented detail. Finally, a significant sample of stars in the outskirts of the Large Magellanic Cloud (LMC) will be studied, providing new light into the debate about the existence of an LMC spheroidal component. These, among other important research goals attainable with the DES stellar data, are discussed in this contribution.
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Han, Z., i Ph Podsiadlowski. "Binary Evolutionary Models". Proceedings of the International Astronomical Union 4, S252 (kwiecień 2008): 349–57. http://dx.doi.org/10.1017/s1743921308023193.
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AbstractIn this talk, we present the general principles of binary evolution and give two examples. The first example is the formation of subdwarf B stars (sdBs) and their application to the long-standing problem of ultraviolet excess (also known as UV-upturn) in elliptical galaxies. The second is for the progenitors of type Ia supernovae (SNe Ia). We discuss the main binary interactions, i.e., stable Roche lobe overflow (RLOF) and common envelope (CE) evolution, and show evolutionary channels leading to the formation of various binary-related objects. In the first example, we show that the binary model of sdB stars of Han et al. (2002, 2003) can reproduce field sdB stars and their counterparts, extreme horizontal branch (EHB) stars, in globular clusters. By applying the binary model to the study of evolutionary population synthesis, we have obtained an “a priori” model for the UV-upturn of elliptical galaxies and showed that the UV-upturn is most likely resulted from binary interactions. This has major implications for understanding the evolution of the UV excess and elliptical galaxies in general. In the second example, we introduce the single degenerate channel and the double degenerate channel for the progenitors of SNe Ia. We give the birth rates and delay time distributions for each channel and the distributions of companion stars at the moment of SN explosion for the single degenerate channel, which would help to search for the remnant companion stars observationally.
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Kalita, Sanjeev, i Chayanika Rabha. "Possible combinations of early and late time cosmologies through BAO scales". European Physical Journal C 83, nr 7 (27.07.2023). http://dx.doi.org/10.1140/epjc/s10052-023-11841-z.
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AbstractThe theoretical scenarios of early universe and late time accelerated expansion constitute an open problem in cosmology. Relative Baryon Acoustic Oscillation (BAO) scales measured by 6dFGS, $$\mathrm SDSS+2dFGRS$$ S D S S + 2 d F G R S , BOSS DR11 Ly$$\alpha $$ α and BOSS DR11 QSO Ly$$\alpha $$ α are used to investigate the parameter spaces of combinations of pre-recombination physics and late time cosmology. For pre-recombination physics we fix $$\mathrm N_{eff}=3$$ N eff = 3 and 4 and incorporate an Early Dark Energy (EDE) component. For late time cosmologies we consider curved $$\Lambda $$ Λ CDM model, Dynamical Dark Energy (DDE) model with CPL parameterisation ($$\omega _0,\omega _1$$ ω 0 , ω 1 ) of equation of state, Coupled Dark Energy (CDE) model with constant coupling and curved DGP brane-world scenario. Combination of a curved $$\Lambda $$ Λ CDM ($$\Omega _{\textrm{k}}\Lambda $$ Ω k Λ CDM) model with $$\mathrm N_{eff}$$ N eff -EDE cosmology is found to be possible. For DDE, the relative BAO scales are achievable through $$\omega _1$$ ω 1 preferring the region $$\omega _1< 0$$ ω 1 < 0 . For $$\mathrm N_{eff}$$ N eff -EDE-CDE, the BAO scales are generated for both dark energy-dark matter and dark matter-dark energy conversion, however with exceptionally large value of dark energy density parameter and constant equation of state with $$\omega _0 > -1$$ ω 0 > - 1 . Curved DGP cosmology ($$\Omega _\textrm{k}$$ Ω k DGP) is found to join with $$N_{\textrm{eff}}$$ N eff -EDE cosmology through curvature parameter $$\Omega _{\mathrm{k(0)}}\in [-0.002, -0.1]$$ Ω k ( 0 ) ∈ [ - 0.002 , - 0.1 ] and cross-over parameter $$\Omega _{\mathrm{r_c}} \in [0.08, 0.45]$$ Ω r c ∈ [ 0.08 , 0.45 ] . Cosmic ages are calculated for the derived parameters of $$\Omega _{\textrm{k}}\Lambda $$ Ω k Λ CDM, flat DDE and $$\Omega _{\textrm{k}}$$ Ω k DGP models and compared with the ages of few globular clusters available in literature. Curved cosmologies are found to be promising.
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Geier, Stephan, Roy H. Østensen, Peter Nemeth, Ulrich Heber, Nicola P. Gentile Fusillo, Boris T. Gänsicke, John H. Telting, Elizabeth M. Green i Johannes Schaffenroth. "Meet the family − the catalog of known hot subdwarf stars". Open Astronomy 26, nr 1 (20.12.2017). http://dx.doi.org/10.1515/astro-2017-0031.
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AbstractIn preparation for the upcoming all-sky data releases of the Gaia mission, we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalog contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques, we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data. As first application of the catalog data, we present the quantitative spectral analysis of 280 sdB and sdOB stars from the Sloan Digital Sky Survey Data Release 7. Combining our derived parameters with state-of-the-art proper motions, we performed a full kinematic analysis of our sample. This allowed us to separate the first significantly large sample of 78 sdBs and sdOBs belonging to the Galactic halo. Comparing the properties of hot subdwarfs from the disk and the halo with hot subdwarf samples from the globular clusters ω Cen and NGC 2808, we found the fraction of intermediate He-sdOBs in the field halo population to be significantly smaller than in the globular clusters.
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Geier, Stephan, Roy H. Østensen, Peter Nemeth, Ulrich Heber, Nicola P. Gentile Fusillo, Boris T. Gänsicke, John H. Telting, Elizabeth M. Green i Johannes Schaffenroth. "Meet the family − the catalog of known hot subdwarf stars". Open Astronomy 26, nr 1 (20.12.2017). http://dx.doi.org/10.1515/astro-2017-0432.
Pełny tekst źródłaStreszczenie:
AbstractIn preparation for the upcoming all-sky data releases of the Gaia mission, we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalog contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques, we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data. As first application of the catalog data, we present the quantitative spectral analysis of 280 sdB and sdOB stars from the Sloan Digital Sky Survey Data Release 7. Combining our derived parameters with state-of-the-art proper motions, we performed a full kinematic analysis of our sample. This allowed us to separate the first significantly large sample of 78 sdBs and sdOBs belonging to the Galactic halo. Comparing the properties of hot subdwarfs from the disk and the halo with hot subdwarf samples from the globular clusters ! Cen and NGC 2808, we found the fraction of intermediate He-sdOBs in the field halo population to be significantly smaller than in the globular clusters.
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Taylor, Dominic J., Andrew C. Mason, Ricardo P. Schiavon, Danny Horta, David M. Nataf, Doug Geisler, Shobhit Kisku i in. "Is Terzan 5 the remnant of a building block of the Galactic bulge? Evidence from APOGEE". Monthly Notices of the Royal Astronomical Society, 8.04.2022. http://dx.doi.org/10.1093/mnras/stac968.
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Abstract It has been proposed that the globular cluster-like system Terzan 5 is the surviving remnant of a primordial building block of the Milky Way bulge, mainly due to the age/metallicity spread and the distribution of its stars in the α-Fe plane. We employ Sloan Digital Sky Survey (SDSS-IV) data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE 2) to test this hypothesis. Adopting a random sampling technique, we contrast the abundances of 10 elements in Terzan 5 stars with those of their bulge field counterparts with comparable atmospheric parameters, finding that they differ at statistically significant levels. Abundances between the two groups differ by more than 1σ in Ca, Mn, C, O, and Al, and more than 2σ in Si and Mg. Terzan 5 stars have lower [α/Fe] and higher [Mn/Fe] than their bulge counterparts. Given those differences, we conclude that Terzan 5 is not the remnant of a major building block of the bulge. We also estimate the stellar mass of the Terzan 5 progenitor based on predictions by the Evolution and Assembly of GaLaxies and their Environments (EAGLE) suite of cosmological numerical simulations, concluding that it may have been as low as ∼3 × 108 M⊙ so that it was likely unable to significantly influence the mean chemistry of the bulge/inner disk, which is significantly more massive (∼1010 M⊙). We briefly discuss existing scenarios for the nature of Terzan 5 and propose an observational test that may help elucidate its origin.