Reconstructing the Pleiades with Gaia EDR3 Heyl, Jeremy; Caiazzo, Ilaria; Richer, Harvey B.
The Astrophysical journal,
02/2022, Letnik:
926, Številka:
2
Journal Article
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Abstract
We search through an eight million cubic parsec volume surrounding the Pleiades star cluster and the Sun to identify both the current and past members of the Pleiades cluster within the Gaia ...EDR3 data set. We find nearly 1300 current cluster members and 289 former cluster candidates. Many of these candidates lie well in front of or behind the cluster from our point of view, so formerly they were considered cluster members, but their parallaxes put them more than 10 pc from the center of the cluster today. Over the past 100 Myr we estimate that the cluster has lost twenty percent of its mass including two massive white dwarf stars and the
α
2
Canum Venaticorum type variable star, 41 Tau. All three white dwarfs associated with the cluster are massive (1.01–1.06
M
⊙
) and have progenitors with main-sequence masses of about six solar masses. Although we did not associate any giant stars with the cluster, the cooling time of the oldest white dwarf of 60 Myr gives a firm lower limit on the age of the cluster.
Abstract
Despite their shared origin, members of globular clusters display star-to-star variations in composition. The observed pattern of element abundances is unique to these stellar environments ...and cannot be fully explained by any proposed mechanism. It remains unclear whether stars form with chemical heterogeneity or inherit it from interactions with other members. These scenarios may be differentiated by the dependence of chemical spread on stellar mass; however, obtaining a sufficiently large mass baseline requires abundance measurements on the lower main sequence, which is too faint for spectroscopy even in the nearest globular clusters. We developed a stellar modeling method to obtain precise chemical abundances for stars near the end of the main sequence from multiband photometry, and we applied it to the globular cluster 47 Tucanae. The computational efficiency is attained by matching chemical elements to the model components that are most sensitive to their abundance. We determined O/Fe for ∼5000 members below the main-sequence knee at the level of accuracy, comparable to the spectroscopic measurements of evolved members in the literature. The inferred distribution disfavors stellar interactions as the origin of chemical spread; however, an accurate theory of accretion is required to draw a more definitive conclusion. We anticipate that future observations of 47 Tucanae with the James Webb Space Telescope will extend the mass baseline of our analysis into the substellar regime. Therefore, we present predicted color–magnitude diagrams and mass–magnitude relations for the brown dwarf members of 47 Tucanae.
We present new measurements of the centers for 65 Milky Way globular clusters. Centers were determined by fitting ellipses to the density distribution within the inner 2' of the cluster center, and ...averaging the centers of these ellipses. The symmetry of clusters was also analyzed by comparing cumulative radial distributions on opposite sides of the cluster across a grid of trial centers. All of the determinations were done with stellar positions derived from a combination of two single-orbit Advanced Camera for Surveys images of the core of the cluster in F606W and F814W. We find that the ellipse-fitting method provides remarkable accuracy over a wide range of core sizes and density distributions, while the symmetry method is difficult to use on clusters with very large cores or low density. The symmetry method requires a larger field or a very sharply peaked density distribution.
Abstract
We have carried out a search for massive white dwarfs (WDs) in the direction of young open star clusters using the Gaia DR2 database. The aim of this survey was (1) to provide robust data ...for new and previously known high-mass WDs regarding cluster membership, (2) to highlight WDs previously included in the initial final mass relation (IFMR) that are unlikely members of their respective clusters according to Gaia astrometry, and (3) to select an unequivocal WD sample that could then be compared with the host clusters’ turnoff masses. All promising WD candidates in each cluster color–magnitude diagram were followed up with spectroscopy from Gemini in order to determine whether they were indeed WDs and derive their masses, temperatures, and ages. In order to be considered cluster members, white dwarfs were required to (1) have proper motions and parallaxes within 2
σ
, 3
σ
, or 4
σ
of those of their potential parent cluster based on how contaminated the field was in their region of the sky, (2) have a cooling age that was less than the cluster age, and (3) have a mass that was broadly consistent with the IFMR. A number of WDs included in current versions of the IFMR turned out to be nonmembers, and a number of apparent members, based on Gaia’s astrometric data alone, were rejected, as their mass and/or cooling times were incompatible with cluster membership. In this way, we developed a highly selected IFMR sample for high-mass WDs that, surprisingly, contained no precursor masses significantly in excess of ∼ 6
M
⊙
.
Based on the width of its main sequence, and an actual observed split when viewed through particular filters, it is widely accepted that 47 Tucanae contains multiple stellar populations. In this ...contribution, we divide the main sequence of 47 Tuc into four color groups, which presumably represent stars of various chemical compositions. The kinematic properties of each of these groups are explored via proper motions, and a strong signal emerges of differing proper-motion anisotropies with differing main-sequence color; the bluest main-sequence stars exhibit the largest proper-motion anisotropy which becomes undetectable for the reddest stars. In addition, the bluest stars are also the most centrally concentrated. A similar analysis for Small Magellanic Cloud stars, which are located in the background of 47 Tuc on our frames, yields none of the anisotropy exhibited by the 47 Tuc stars. We discuss implications of these results for possible formation scenarios of the various populations.
The initial-final mass relation represents a mapping between the mass of a white dwarf remnant and the mass that the hydrogen-burning main-sequence star that created it once had. The empirical ...relation thus far has been constrained using a sample of image40 stars in young open clusters, ranging in initial mass from image2.75 to 7 image, and shows a general trend that connects higher mass main-sequence stars with higher mass white dwarfs. In this paper, we present CFHT CFH12K photometric and Keck LRIS multiobject spectroscopic observations of a sample of 22 white dwarfs in two older open clusters, NGC 7789 (image Gyr) and NGC 6819 (image Gyr). We measure masses for the highest signal-to-noise ratio spectra by fitting the Balmer lines to atmosphere models and place the first direct constraints on the low- mass end of the initial-final mass relation. Our results indicate that the observed general trend at higher masses continues down to low masses, with image main-sequence stars forming image white dwarfs. When added to our new data from the very old cluster NGC 6791, the relation is extended down to image (corresponding to image). This extension of the relation represents a fourfold increase in the total number of hydrogen-burning stars for which the integrated mass loss can now be calculated from empirical data, assuming a Salpeter initial mass function. The new leverage at the low-mass end is used to derive a purely empirical initial-final mass relation. The sample of white dwarfs in these clusters also shows several interesting systems that we discuss further: a DB (helium) white dwarf, a magnetic white dwarf, a DAB (mixed hydrogen/helium atmosphere or a double degenerate DA+DB) white dwarf(s), and two possible equal-mass da double degenerate binary systems.
We have searched the Gaia DR2 catalog for previously unknown hot white dwarfs in the direction of young open star clusters. The aim of this experiment was to try and extend the initial-final mass ...relation (IFMR) to somewhat higher masses, potentially challenging the Chandrasekhar limit currently thought to be around 1.38 M . We discovered a particularly interesting white dwarf in the direction of the young ∼150 Myr old cluster Messier 47 (NGC 2422). All Gaia indicators (proper motion, parallax, location in the Gaia color-magnitude diagram) suggest that it is a cluster member. Its spectrum, obtained from Gemini-South, yields a number of anomalies: it is a DB (helium-rich atmosphere) white dwarf, it has a large magnetic field (2.5 MG), is of high mass (∼1.06 M ), and its colors are very peculiar-particularly the redder ones (r, i, z and y), which suggests that it may have a late-type companion. This may be the only magnetized, detached binary white dwarf with a non-degenerate companion of any spectral type known in or out of a star cluster. If the white dwarf is a cluster member, as all indicators suggest, its progenitor had a mass just over 6 M . It may, however, be telling an even more interesting story than the one related to the IFMR, one about the origin of stellar magnetic fields, SNe I, and gravitational waves from low-mass stellar systems.
Abstract
We searched the Gaia DR3 database for ultramassive white dwarfs with kinematics consistent with having escaped the nearby Hyades open cluster, identifying three such candidates. Two of these ...candidates have masses estimated from Gaia photometry of approximately 1.1 solar masses; their status as products of single-stellar evolution that have escaped the cluster was deemed too questionable for immediate follow-up analysis. The remaining candidate has an expected mass >1.3 solar masses, significantly reducing the probability of it being an interloper. Analysis of follow-up Gemini GMOS spectroscopy for this source reveals a nonmagnetized hydrogen atmosphere white dwarf with a mass and age consistent with having formed from a single star. Assuming a single-stellar-evolution formation channel, we estimate a 97.8% chance that the candidate is a true escapee from the Hyades. With a determined mass of 1.317 solar masses, this is potentially the most massive known single-evolution white dwarf and is by far the most massive with a strong association with an open cluster.
Abstract
We searched through the entire Gaia EDR3 candidate white dwarf catalog for stars with proper motions and positions that are consistent with them having escaped from the Alpha Persei cluster ...within the past 81 Myr, the age of the cluster. In this search we found five candidate white dwarf escapees from Alpha Persei and obtained spectra for all of them. We confirm that three are massive white dwarfs sufficiently young to have originated in the cluster. All these are more massive than any white dwarf previously associated with a cluster using Gaia astrometry, and possess some of the most massive progenitors. In particular, the white dwarf Gaia EDR3 4395978097863572, which lies within 25 pc of the cluster center, has a mass of about 1.20 solar masses and evolved from an 8.5 solar-mass star, pushing the upper limit for white dwarf formation from a single massive star, while still leaving a substantial gap between the resulting white dwarf mass and the Chandrasekhar mass.
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