- ID:
- ivo://CDS.VizieR/J/ApJ/764/73
- Title:
- HST VI photometry of HD 97950 cluster members stars
- Short Name:
- J/ApJ/764/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep Hubble Space Telescope/Wide Field and Planetary Camera 2 photometry of the young HD 97950 star cluster in the giant H II region NGC 3603. The data were obtained in 1997 and 2007 permitting us to derive membership based on proper motions of the stars. Our data are consistent with an age of 1 Myr for the HD 97950 cluster. A possible age spread, if present in the cluster, appears to be small. The global slope of the incompleteness-corrected mass function for member stars within 60" is {Gamma}=-0.88+/-0.15, which is flatter than the value of a Salpeter slope of -1.35. The radially varying mass function shows pronounced mass segregation ranging from slopes of -0.26 +/-0.32 in the inner 5" to -0.94+/-0.36 in the outermost annulus (40"-60"). Stars more massive than 50M_{sun}_ are found only in the cluster center. The {Lambda} minimum spanning tree technique confirms significant mass segregation down to 30M_{sun}_. The dependence of {Lambda} on mass, i.e., that high-mass stars are more segregated than low-mass stars, and the (weak) dependence of the velocity dispersion on stellar mass might imply that the mass segregation is dynamical in origin. While primordial segregation cannot be excluded, the properties of the mass segregation indicate that dynamical mass segregation may have been the dominant process for segregation of high-mass stars.
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- ID:
- ivo://CDS.VizieR/J/ApJ/730/78
- Title:
- Hubble and Spitzer photometry of NGC 602
- Short Name:
- J/ApJ/730/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical (HST/ACS F555W, F814W, and SMARTS/ANDICAM V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8um and MIPS 24um). Combining this with Infrared Survey Facility near-infrared photometry (J, H, Ks), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared. We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ~565 PMS candidates, low-mass Stage III YSOs. We characterize ~40 YSOs by fitting their spectral energy distributions to a grid of models (Robitaille et al. 2007ApJS..169..328R) to derive luminosities, masses, and evolutionary phase (Stages I-III). The higher resolution HST images reveal that ~70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star formation rate of ~0.2-1.0M_{sun}_/yr/kpc^2^, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region.
- ID:
- ivo://CDS.VizieR/J/A+A/481/661
- Title:
- Hyades brown dwarfs and very low mass stars
- Short Name:
- J/A+A/481/661
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a search for brown dwarfs (BDs) and very low mass (VLM) stars in the 625Myr-old Hyades cluster in order to derive the cluster's mass function across the stellar-substellar boundary. We performed a deep (I=23, z=22.5) photometric survey over 16deg^2^ around the cluster center and followed up with K-band photometry to measure the proper motion of candidate members and with optical and near-IR spectroscopy of probable BD and VLM members.
- ID:
- ivo://CDS.VizieR/J/AJ/80/379
- Title:
- Hyades cluster: motion, membership, and distance
- Short Name:
- J/AJ/80/379
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New absolute proper motions referred directly to external galaxies, photographic photometry, and cluster membership probabilities have been determined for over 600 faint stars in the Hyades region. These have been used to investigate the Hyades convergent point and distance. A detailed review of the foundations of the convergent-point method, its applicability to the Hyades, the several mathematical variations of the method, and its possible role in producing the apparent discrepancy between previous Hyades proper motion results and "secondary" Hyades distance indicators, has been carried out. The convergent-point method, as applied to the Hyades, is entirely valid, and cannot be the source of any significant error in the Hyades distance. Systematic errors in meridian circle proper motions are implicated as the cause of the observed Hyades distance discrepancy. The convergent-point analysis of the new absolute Hyades proper motions represents the first Hyades distance determination independent of all meridian circle proper motion systems. The resulting Hyades distance modulus is m-M=3.42, significantly greater than all previous values from proper motions, and in agreement with predictions of the Hyades distance from stellar structure theory, and with the results of "secondary" distance indicators. Incorporating this value, the most likely value of the mean Hyades distance modulus from all sources is m-M=3.29+/-0.08. The quoted error represents a larger and more realistic estimate of the true errors than has been previously stated. Significant effects of the increased Hyades distance on the cosmic distance scale and other questions of general astronomical importance are briefly discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/243/386
- Title:
- Hyades members distances
- Short Name:
- J/A+A/243/386
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Distances for 145 Hyades members in an extended region of the Hyades cluster were derived on the basis of new, highly accurate proper motions obtained from work on the catalogues FK5 and PPM. The cluster membership on the stars has been discussed and a few new candidates are proposed. From a selected subset of our sample we have obtained the convergence point {alpha}=6h30.7m+/-1.7m=97deg41'+/-25', {delta}=5deg59'+/-11'. Combining this point with the mean cluster radial velocity of 39.1km/s by Detweiler et al. (1984AJ.....89.1038D) one find the galactic space velocity (U, V, W)=(-42.02, -20.12, -1.04)km/s. The galactic coordinates of the centre of our sample are (X, Y, Z)=(-44.3, +0.5, -18.2)pc. The distance of this centre from the Sun is 47.9+/-0.8pc corresponding to a modulus m-M=3.40+/-0.04mag. Individual distance moduli, coordinates and velocity residuals per star are given. The Hyades main sequence has been constructed in the range B-V<1.2mag and it is presented analytically as well as by tabular values. The dispersion {sigma}(M_v_)=0.14mag of the absolute magnitudes about the main sequence indicates its high internal accuracy.
406. Hyades membership
- ID:
- ivo://CDS.VizieR/J/A+A/331/81
- Title:
- Hyades membership
- Short Name:
- J/A+A/331/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use absolute trigonometric parallaxes from the Hipparcos Catalogue (Cat. <I/239>) to determine individual distances to members of the Hyades cluster, from which the 3-dimensional structure of the cluster can be derived. Inertially-referenced proper motions are used to rediscuss distance determinations based on convergent-point analyses. A combination of parallaxes and proper motions from Hipparcos, and radial velocities from ground-based observations, are used to determine the position and velocity components of candidate members with respect to the cluster centre, providing new information on cluster membership: 13 new candidate members within 20pc of the cluster centre have been identified. Farther from the cluster centre there is a gradual merging between certain cluster members and field stars, both spatially and kinematically. Within the cluster, the kinematical structure is fully consistent with parallel space motion of the component stars with an internal velocity dispersion of about 0.3km/s. The spatial structure and mass segregation are consistent with N-body simulation results, without the need to invoke expansion, contraction, rotation, or other significant perturbations of the cluster. The quality of the individual distance determinations permits the cluster zero-age main sequence to be accurately modelled. The helium abundance for the cluster is determined to be Y=0.26+/-0.02 which, combined with isochrone modelling including convective overshooting, yields a cluster age of 625+/-50Myr. The distance to the observed centre of mass (a concept meaningful only in the restricted context of the cluster members contained in the Hipparcos Catalogue) is 46.34+/-0.27pc, corresponding to a distance modulus m-M=3.33+/-0.01mag for the objects within 10pc of the cluster centre (roughly corresponding to the tidal radius). This distance modulus is close to, but significantly better determined than, that derived from recent high-precision radial velocity studies, somewhat larger than that indicated by recent ground-based trigonometric parallax determinations, and smaller than those found from recent studies of the cluster convergent point. These discrepancies are investigated and explained.
- ID:
- ivo://CDS.VizieR/J/ApJ/448/683
- Title:
- Hyades RASS observations
- Short Name:
- J/ApJ/448/683
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a complete X-ray survey of the Hyades cluster region using the ROSAT All-Sky Survey (RASS). Our survey covers over 900deg^2^ of the sky. Over 185 optically identified Hyades were detected down to a limiting X-ray luminosity of ~1-2x10^28^ergs/s (0.1-1.8keV); among solar-like stars, i.e., main-sequence stars of spectral type G, the RASS detection rate is ~90%. The presence of many binary systems in the cluster is a key factor influencing the X-ray luminosity function. Short-period (~ a few days or less) binaries are anomalously X-ray bright, as might be expected; however, the X-ray luminosity functions of K and possibly M binaries of all types are significantly different from their single counterparts, confirming the results of Pye et al. (1994MNRAS.266..798P) for a smaller K star sample drawn from deep ROSAT pointings. Comparison with Einstein Observatory studies of a subset of Hyades stars demonstrates a general lack of significant (> a factor of 2) long-term X-ray variability. This may be the result of the dominance of a small-scale, turbulent dynamo in the younger Hyades stars compared to the large-scale, cyclic dynamo observed in the Sun.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A7
- Title:
- Hyades single stars fiducial photometry
- Short Name:
- J/A+A/585/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Age and mass determinations for isolated stellar objects remain model-dependent. While stellar interior and atmospheric theoretical models are rapidly evolving, we need a powerful tool to test them. Open clusters are good candidates for this role. We aim to create a fiducial sequence of stellar objects for testing stellar and atmospheric models. We complement previous studies on the Hyades multiplicity by Lucky Imaging observations with the AstraLux Norte camera. This allows us to exclude possible binary and multiple systems with companions outside 2-7AU separation and to create a "single-star sequence" for the Hyades. The sequence encompasses 250 main-sequence stars ranging from A5V to M6V. Using the "Tool for Astrophysical Data Analysis" (TA-DA), we create various theoretical isochrones applying different combinations of interior and atmospheric models. We compare the isochrones with the observed Hyades single-star sequence on J vs. J-Ks, J vs. J-H and Ks vs. H-Ks color-magnitude diagrams. As a reference we also compute absolute fluxes and magnitudes for all stars from X-ray to mid-infrared based on photometric measurements available in the literature (ROSAT X-ray, GALEX UV, APASS gri, 2MASS JHKs, and WISE W1 to W4). We find that combinations of both PISA and DARTMOUTH stellar interior models with BT-Settl 2010 atmospheric models describe the observed sequence well. We use PISA in combination with BT-Settl 2010 models to derive theoretical predictions for physical parameters (Teff, mass, logg) of 250 single stars in the Hyades. The full sequence covers the mass range 0.13 to 2.3M_{sun}_, and effective temperatures between 3060K and 8200K. Conclusions. Within the measurement uncertainties, the current generation of models agree well with the single-star sequence. The primary limitations are the uncertainties in the measurement of the distance to individual Hyades members, and uncertainties in the photometry. Gaia parallaxes, photometry and spectroscopy will greatly reduce the uncertainties in particular at the lowest mass range, and will enable us to test model predictions with greater confidence. Additionally, a small (~0.05mag) systematic offset can be noted on J vs. J-K and K vs. H-K diagrams - the observed sequence is shifted to redder colors from the theoretical predictions.
- ID:
- ivo://CDS.VizieR/J/A+A/621/L2
- Title:
- Hyades tidal tails revealed by Gaia DR2
- Short Name:
- J/A+A/621/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Within a 200pc sphere around the Sun, we search for the Hyades tidal tails in the Gaia DR2 dataset. We used a modified convergent-point method to search for stars with space velocities close to the space velocity of the Hyades cluster. We find a clear indication for the existence of the Hyades tidal tails, a leading tail extending up to 170pc from the centre of the Hyades with 292 stars (36 contaminants), and a trailing tail up to 70pc with 237 stars (32 contaminants). A comparison with an N-body model of the cluster and its tails shows remarkably good coincidence. Five white dwarfs are found in the tails.
- ID:
- ivo://CDS.VizieR/J/A+A/621/L3
- Title:
- Hyades tidal tails with Gaia DR2
- Short Name:
- J/A+A/621/L3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of two well-defined tidal tails emerging from the Hyades star cluster. The tails were detected in Gaia DR2 data by selecting cluster members in the 3D galactocentric cylindrical velocity space. The robustness of our member selection is reinforced by the fact that the sources depict an almost noiseless, coeval stellar main sequence in the observational Hertzsprung-Russel diagram. The spatial arrangement of the selected members represents a highly flattened shape with respect to the direction of movement along the clusters' orbit in the Galaxy. The size of the entire structure, within the limits of the observations, measures about 200pc in its largest extent, while being only about 25pc thick. This translates into an on-sky extent of well beyond 100deg. Intriguingly, a top-down view on the spatial distribution reveals a distinct S-shape, reminiscent of tidal tails that have been observed for globular clusters and also of tails that were modeled for star clusters bound to the Galactic disk. Even more remarkable, the spatial arrangement as well as the velocity dispersion of our source selection is in excellent agreement with previously published theoretical predictions for the tidal tails of the Hyades. An investigation into observed signatures of equipartition of kinetic energy, that is, mass segregation, remains unsuccessful, most likely because of the sensitivity limit for radial velocity measurements with Gaia.