- 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.
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- 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.
- 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.
- ID:
- ivo://CDS.VizieR/II/362
- Title:
- i-band variability of YSOs
- Short Name:
- II/362
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an i-band photometric study of over 800 young stellar objects in the OB association Cep OB3b, which samples timescales from 1 minute to ten years. Using structure functions we show that on all timescales (tau) there is a monotonic decrease in variability from Class I to Class II through the transition disc (TD) systems to Class III, i.e. the more evolved systems are less variable. The Class Is show an approximately power-law increase (tau^0.8^) in variability from timescales of a few minutes to ten years. The Class II, TDs and Class III systems show a qualitatively different behaviour with most showing a power-law increase in variability to a timescale corresponding to the rotational period of the star, with little additional variability beyond that timescale. However, about a third of the Class IIs show lower overall variability, but their variability is still increasing at 10 years. This behaviour can be explained if all Class IIs have two primary components to their variability. The first is an underlying roughly power-law variability spectrum, which evidence from the infrared suggests is driven by accretion rate changes. The second component is an approximately sinusoidal and results from the rotation of the star. We suggest that the systems with dominant longer-timescale variability have a smaller rotational modulation either because they are seen at low inclinations or have more complex magnetic field geometries. We derive a new way of calculating structure functions for large simulated datasets (the "fast structure function"), based on fast Fourier transforms.
358. IC 4665
- ID:
- ivo://CDS.VizieR/J/AJ/105/1441
- Title:
- IC 4665
- Short Name:
- J/AJ/105/1441
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a combined astrometric, photometric, and spectroscopic program to identify members of the open cluster IC 4665 are presented. Numerous new proper motion/photometric candidate members and at least 23 M dwarfs with H-alpha emission have been identified. A reanalysis of IC 4665's age using different methods yields conflicting results ranging from approx. 3x10^7^ yr to the age of the Pleiades. This study provides a list of candidate cluster members in the intermediate and low-mass regime of this cluster. Future spectroscopic observations of these candidates should eventually identify true cluster members. The results of new echelle observations of some candidates and the photometric monitoring of one apparent cluster member are given in an appendix.
- ID:
- ivo://CDS.VizieR/J/AJ/116/1801
- Title:
- IC 4996 CCD photometry
- Short Name:
- J/AJ/116/1801
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a UBV CCD photometric study of the cluster IC 4996 are presented. We obtain new values for the cluster parameters: E(B-V)=0.71+/-0.08, V_0_-M_V_=11.9+/-0.1, and age=(7.5+/-3)x10^6^yr. The combined evidence from the photometric diagrams suggests the presence of a number of premain-sequence (PMS) cluster members with spectral types ~A0 to F5. The interpretation of these objects as PMS candidates is further supported by independent results from CCD uvbyH{beta} observations. If confirmed, these stars would bridge the existing gap in the sample of PMS stars, between the coolest Herbig AeBe stars (HAeBe), and the hottest T Tauri stars. These PMS candidates are located some 0.5 and 1 mag above the main sequence in the V-(B-V) diagram, around the location of spectral types AF. This feature, together with their locations in the (U-B)-(B-V) diagram and the interpretation that they are PMS members, suggest an additional reddening law with a slope {alpha}=E(U-B)/E(B-V)~0.55, probably caused by circumstellar material.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/3674
- Title:
- IC 348 circumstellar discs ALMA data
- Short Name:
- J/MNRAS/478/3674
- Date:
- 10 Dec 2021 00:10:52
- Publisher:
- CDS
- Description:
- We present a 1.3mm continuum survey of the young (2-3Myr) stellar cluster IC 348 that lies at a distance of 310pc and is dominated by low-mass stars (M*~0.1-0.6M_{sun}_). We observed 136 Class II sources (discs that are optically thick in the infrared) at 0.8arcsec (200au) resolution with a 3{sigma} sensitivity of ~0.45mJy (M_dust_~1.3M_{Earth}_). We detect 40 of the targets and construct a mm-continuum luminosity function. We compare the disc mass distribution in IC 348 to those of younger and older regions, taking into account the dependence on stellar mass. We find a clear evolution in disc masses from 1 to 5-10Myr. The disc masses in IC 348 are significantly lower than those in Taurus (1-3Myr) and Lupus (1-3Myr), similar to those of Chamaleon I, (2-3Myr) and {sigma} Ori (3-5Myr) and significantly higher than in Upper Scorpiusrpius (5-10Myr). About 20 discs in our sample (~5 percent of the cluster members) have estimated masses (dust+gas)>1M_Jup_ and hence might be the precursors of giant planets in the cluster. Some of the most massive discs include transition objects with inner opacity holes based on their infrared Spectral Energy Distribution (SEDs). From a stacking analysis of the 96 non-detections, we find that these discs have a typical dust mass of just <=0.4M_{Earth}_, even though the vast majority of their infrared SEDs remain optically thick and show little signs of evolution. Such low-mass discs may be the precursors of the small rocky planets found by Kepler around M-type stars.
