Hyades Cluster Research Articles

Exploring the substellar population in the Hyades open cluster

Aims. Our aim is to identify substellar members of the nearby Hyades open star cluster to determine the photometric and spectroscopic properties of brown dwarfs at moderately old ages and extend our knowledge of the substellar mass function of the cluster. Methods. We cross-matched the 2MASS and WISE public catalogues and measured proper motions to identify low-mass stars and brown dwarf member candidates in an area of a radius of ten degrees around the central region of the Hyades cluster. We employed astrometric and photometric criteria, Gaia data, and a maximum likelihood method developed by our group to estimate distances. We selected 36 objects that are candidate Hyades members, 21 of which have not been reported previously. Results. We have identified 21 new Hyades member candidates that are placed at the lower end of the main sequence. The photometry of 9 candidates places them in the substellar regime, and 2 are at the L/T transition. We also recovered a number of L dwarfs from earlier surveys. Finally, we calculated the mass function for the low-mass population of the cluster and found that the Hyades cluster might have lost 60%–80% of its substellar members.

Spectroscopic and astrometric radial velocities: Hyades as a benchmark

We study the accuracy of spectroscopic RVs by comparing spectroscopic and astrometric RVs for stars of the Hyades open cluster. Rather accurate astrometric RVs are available for the Hyades' stars, based on Hipparcos and on the first Gaia data release. We obtained HARPS spectra for a large sample of Hyades stars, and homogeneously analysed them. After cleaning the sample from binaries, RV variables, and outliers, 71 stars remained. The distribution of the observed RV difference (spectroscopic -- astrometric) is skewed and depends on the star right ascension. This is consistent with the Hyades cluster rotating at 42.3 +/- 10 m/s/pc. The two Hyades giants in the sample show, as predicted by gravitational redshift (GR), a spectroscopic RV that is blue-shifted with respect to the dwarfs, and the empirical GR slope is of 626 +/- 131 m/s, in agreement with the theoretical prediction. The difference between spectroscopic and astrometric RVs is very close to zero, within the uncertainties. In particular, the mean difference is of -33 m/s and the median is of -16 m/s when considering the Gaia-based RVs (corrected for cluster rotation), with a sigma of 347 m/s, very close to the expected cluster velocity dispersion. We also determine a new value of the cluster centroid spectroscopic RV: 39.36 +/- 0.26 km/s. The spectroscopic RV measurements are expected, from simulations, to depend on stellar rotation, but our data do not confirm these predictions. We finally discuss other phenomena that can influence the RV difference, such as cluster expansion, stellar activity, general relativity, and Galactic potential. Clusters within the reach of current telescopes are expected to show differences of several hundreds m/s, depending on their position in the Galaxy.

Zodiacal Exoplanets in Time (ZEIT). VII. A Temperate Candidate Super-Earth in the Hyades Cluster

Abstract Transiting exoplanets in young open clusters present opportunities to study how exoplanets evolve over their lifetimes. Recently, significant progress detecting transiting planets in young open clusters has been made with the K2 mission, but so far all of these transiting cluster planets orbit close to their host stars, so planet evolution can only be studied in a high-irradiation regime. Here, we report the discovery of a long-period planet candidate, called HD 283869 b, orbiting a member of the Hyades cluster. Using data from the K2 mission, we detected a single transit of a super-Earth-sized (1.96 ± 0.12 R ⊕) planet candidate orbiting the K-dwarf HD 283869 with a period longer than 72 days. As we only detected a single-transit event, we cannot validate HD 283869 b with high confidence, but our analysis of the K2 images, archival data, and follow-up observations suggests that the source of the event is indeed a transiting planet. We estimated the candidate’s orbital parameters and find that if real, it has a period P ≈ 100 days and receives approximately Earth-like incident flux, giving the candidate a 71% chance of falling within the circumstellar habitable zone. If confirmed, HD 283869 b would have the longest orbital period, lowest incident flux, and brightest host star of any known transiting planet in an open cluster, making it uniquely important to future studies of how stellar irradiation affects planetary evolution.

Membership determination of open clusters based on a spectral clustering method

Abstract We present a spectral clustering (SC) method aimed at segregating reliable members of open clusters in multi-dimensional space. The SC method is a non-parametric clustering technique that performs cluster division using eigenvectors of the similarity matrix; no prior knowledge of the clusters is required. This method is more flexible in dealing with multi-dimensional data compared to other methods of membership determination. We use this method to segregate the cluster members of five open clusters (Hyades, Coma Ber, Pleiades, Praesepe, and NGC 188) in five-dimensional space; fairly clean cluster members are obtained. We find that the SC method can capture a small number of cluster members (weak signal) from a large number of field stars (heavy noise). Based on these cluster members, we compute the mean proper motions and distances for the Hyades, Coma Ber, Pleiades, and Praesepe clusters, and our results are in general quite consistent with the results derived by other authors. The test results indicate that the SC method is highly suitable for segregating cluster members of open clusters based on high-precision multi-dimensional astrometric data such as Gaia data.

A spectroscopic survey of the youngest field stars in the solar neighborhood

Context. Star formation in the solar neighborhood is mainly traced by young stars in open clusters, associations, and in the field, which can be identified, for example, by their X-ray emission. The determination of stellar parameters for the optical counterparts of X-ray sources is crucial for a full characterization of these stars. Aims. This work extends the spectroscopic study of the RasTyc sample, obtained by the cross-correlation of the Tycho and ROSAT All-Sky Survey catalogs, to stars fainter than V = 9.5 mag and aims to identify sparse populations of young stars in the solar neighborhood. Methods. We acquired 625 high-resolution spectra for 443 presumably young stars with four different instruments in the northern hemisphere. The radial and rotational velocity (vsini) of our targets were measured by means of the cross-correlation technique, which is also helpful to discover single-lined (SB1), double-lined spectroscopic binaries (SB2), and multiple systems. We used the code ROTFIT to perform an MK spectral classification and to determine the atmospheric parameters (Teff, logg, [Fe/H]) and vsini of the single stars and SB1 systems. For these objects, we used the spectral subtraction of slowly rotating templates to measure the equivalent widths of the Hα and Li I 6708 Å lines, which enabled us to derive their chromospheric activity level and lithium abundance. We made use of Gaia DR1 parallaxes and proper motions to locate the targets in the Hertzsprung-Russell (HR) diagram and to compute the space velocity components of the youngest objects. Results. We find a remarkable percentage (at least 35%) of binaries and multiple systems. On the basis of the lithium abundance, the sample of single stars and SB1 systems appears to be mostly (~60%) composed of stars younger than the members of the UMa cluster. The remaining sources are in the age range between the UMa and Hyades clusters (~20%) or older (~20%). In total, we identify 42 very young (PMS-like) stars, which lie above or very close to the Pleiades upper envelope of the lithium abundance. A significant percentage (~12%) of evolved stars (giants and subgiants) is also present in our sample. Some of these stars (~36%) are also lithium rich (A(Li) > 1.4).

The Lithium Depletion Boundary and the Age of the Hyades Cluster∗

Abstract Determination of the lithium depletion boundary (LDB), i.e., the observational limit below which the cores of very low-mass objects do not reach high enough temperatures for Li destruction, has been used to obtain ages for several open clusters and stellar associations younger than 200 Myr—which until now has been considered the practical upper limit on the range of applicability of this method. In this work, we show that the LDB method can be extended to significant older ages than previously thought. Intermediate resolution optical spectra of six L-type candidate members in the Hyades cluster obtained using Optical System for Imaging and Low Resolution Integrated Spectroscopy at the 10.4 m Gran Telescopio Canarias are presented. The 670.8 nm resonance doublet is clearly detected only in the two faintest and coolest of these objects, which are classified as L3.5 to L4 brown dwarf (BD) cluster members with luminosities around 10−4 solar. Lithium depletion factors are estimated for our targets with the aid of synthetic spectra and they are compared with predictions from evolutionary models. An LDB age of 650 ± 70 Myr for the Hyades provides a consistent description of our data using a set of state-of-the-art evolutionary models for BDs calculated by Baraffe et al.

Spots and the Activity of Stars in the Hyades Cluster from Observations with the Kepler Space Telescope (K2)

Observations of the K2 mission (continuing the program of the Kepler Space Telescope) are used to estimate the spot coverage S (the fractional area of spots on the surface of an active star) for stars of the Hyades cluster. The analysis is based on data on the photometric variations of 47 confirmed single cluster members, together with their atmospheric parameters, masses, and rotation periods. The resulting values of S for these Hyades objects are lower than those stars of the Pleiades cluster (on average, by ΔS ~ 0.05−0.06). A comparison of the results of studies of cool, low-mass dwarfs in the Hyades and Pleiades clusters, as well as the results of a study of 1570 M stars from the main field observed in the Kepler SpaceMission, indicates that the Hyades stars are more evolved than the Pleiades stars, and demonstrate lower activity. The activity of seven solar-type Hyades stars (S = 0.013 ± 0.006) almost approaches the activity level of the present-day Sun, and is lower than the activity of solar-mass stars in the Pleiades (S = 0.031 ± 0.003). Solar-type stars in the Hyades rotate faster than the Sun (〈P〉 = 8.6 d ), but slower than similar Pleiades stars.

A survey for low-mass stellar and substellar members of the Hyades open cluster

Context. Unlike young open clusters (with ages < 250 Myr), the Hyades cluster (age ~ 600 Myr) has a clear deficit of very low-mass stars (VLM) and brown dwarfs (BD). Since this open cluster has a low stellar density and covers several tens of square degrees on the sky, extended surveys are required to improve the statistics of the VLM/BD objects in the cluster. Aim. We search for new VLM stars and BD candidates in the Hyades cluster to improve the present-day cluster mass function down to substellar masses. Methods. An imaging survey of the Hyades with a completeness limit of 21.m5 in the R band and 20.m5 in the I band was carried out with the 2k × 2k CCD Schmidt camera at the 2 m Alfred Jensch Telescope in Tautenburg. We performed a photometric selection of the cluster member candidates by combining results of our survey with 2MASS JHKs photometry Results. We present a photometric and proper motion survey covering 23.4 deg2 in the Hyades cluster core region. Using optical/IR colour-magnitude diagrams, we identify 66 photometric cluster member candidates in the magnitude range 14.m7 < I < 20.m5. The proper motion measurements are based on several all-sky surveys with an epoch difference of 60–70 yr for the bright objects. The proper motions allowed us to discriminate the cluster members from field objects and resulted in 14 proper motion members of the Hyades. We rediscover Hy 6 as a proper motion member and classify it as a substellar object candidate (BD) based on the comparison of the observed colour-magnitude diagram with theoretical model isochrones. Conclusions. With our results, the mass function of the Hyades continues to be shallow below ~0.15 M⊙ indicating that the Hyades have probably lost their lowest mass members by means of dynamical evolution. We conclude that the Hyades core represents the “VLM/BD desert” and that most of the substeller objects may have already left the volume of the cluster.

K2-136: A Binary System in the Hyades Cluster Hosting a Neptune-sized Planet

Abstract We report the discovery of a Neptune-size planet ( ) in the Hyades Cluster. The host star is in a binary system, comprising a K5V star and M7/8V star with a projected separation of 40 au. The planet orbits the primary star with an orbital period of 17.3 days and a transit duration of 3 hrs. The host star is bright (V = 11.2, J = 9.1) and so may be a good target for precise radial velocity measurements. K2-136A c is the first Neptune-sized planet to be found orbiting in a binary system within an open cluster. The Hyades is the nearest star cluster to the Sun, has an age of 625–750 Myr, and forms one of the fundamental rungs in the distance ladder; understanding the planet population in such a well-studied cluster can help us understand and set constraints on the formation and evolution of planetary systems.

Zodiacal Exoplanets in Time (ZEIT). VI. A Three-planet System in the Hyades Cluster Including an Earth-sized Planet

Abstract Planets in young clusters are powerful probes of the evolution of planetary systems. Here we report the discovery of three planets transiting EPIC 247589423, a late-K dwarf in the Hyades (≃800 Myr) cluster, and robust detection limits for additional planets in the system. The planets were identified from their K2 light curves as part of our survey of young clusters and star-forming regions. The smallest planet has a radius comparable to Earth ( ), making it one of the few Earth-sized planets with a known, young age. The two larger planets are likely a mini-Neptune and a super-Earth, with radii of and , respectively. The predicted radial velocity signals from these planets are between 0.4 and 2 m s−1, achievable with modern precision RV spectrographs. Because the target star is bright (V = 11.2) and has relatively low-amplitude stellar variability for a young star (2–6 mmag), EPIC 247589423 hosts the best known planets in a young open cluster for precise radial velocity follow-up, enabling a robust test of earlier claims that young planets are less dense than their older counterparts.

Far beyond the Sun – I. The beating magnetic heart in Horologium

A former member of the Hyades cluster, $\iota$ Horologii ($\iota$ Hor) is a planet-hosting Sun-like star which displays the shortest coronal activity cycle known to date ($P_{\rm cyc}\sim$ 1.6 yr). With an age of $\sim$$625$ Myr, $\iota$ Hor is also the youngest star with a detected activity cycle. The study of its magnetic properties holds the potential to provide fundamental information to understand the origin of cyclic activity and stellar magnetism in late-type stars. In this series of articles, we present the results of a comprehensive project aimed at studying the evolving magnetic field in this star and how this evolution influences its circumstellar environment. This paper summarizes the first stage of this investigation, with results from a long-term observing campaign of $\iota$ Hor using ground-based high-resolution spectropolarimetry. The analysis includes precise measurements of the magnetic activity and radial velocity of the star, and their multiple time-scales of variability. In combination with values reported in the literature, we show that the long-term chromospheric activity evolution of $\iota$ Hor follows a beating pattern, caused by the superposition of two periodic signals of similar amplitude at $P_{1} \simeq 1.97 \pm 0.02$ yr and $P_{2} \simeq 1.41 \pm 0.01$ yr. Additionally, using the most recent parameters for $\iota$ Hor b in combination with our activity and radial velocity measurements, we find that stellar activity dominates the radial velocity residuals, making the detection of additional planets in this system challenging. Finally, we report here the first measurements of the surface longitudinal magnetic field strength of $\iota$ Hor, which displays varying amplitudes within $\pm4$ G and served to estimate the rotation period of the star ($P_{\rm rot} =~7.70^{+0.18}_{-0.67}$ d).

On the Iron Abundance Anomaly in K-dwarf and Hyades Stars

Abstract Using standard 1D-LTE model atmosphere analysis, we provide an in-depth investigation of iron abundance as derived from neutral and singly ionization iron lines (Fe i, ii) in nearby star clusters. Specifically, we replicate the discrepancy regarding Δ[Fe/H], wherein the difference of Fe ii–Fe i increases for stars of the same cluster with decreasing T eff, reaching an astonishing 1.0 dex at T eff ∼ 4000 K. Previous studies have investigated this anomaly in the Pleiades and Hyades clusters with no concrete solution. In this analysis, we probe two samples: 63 wide binary field stars where the primary star is of Sun-like temperatures and the secondary is a K-dwarf, ranging from 4231 K ≤ T eff ≤ 6453 K, and 33 Hyades stars of temperatures 4268 K ≤ T eff ≤ 6072 K. Previous studies have found discrepancies on the order of 1.0 dex. However, we find that these studies have neglected line-blending effects of certain Fe ii lines, namely λ = {4508.29 Å, 4993.34 Å, 5197.58 Å, 5325.55 Å, 5425.26 Å, 6456.38 Å}. When these lines are removed from the line-list, we find Δ[Fe/H] decreases to ∼0.6 dex in the field binaries and ∼0.3 dex in the Hyades. The reason for this remaining trend is investigated by probing NLTE effects, as well as age and activity considerations using Ca ii H+K emission and Li absorption, but these results appear to be small to negligible.

K2-111 b − a short period super-Earth transiting a metal poor, evolved old star

The star EPIC 210894022 has been identified from a light curve acquired through the K2 space mission as possibly orbited by a transiting planet. Our aim is to confirm the planetary nature of the object and derive its fundamental parameters. We combine the K2 photometry with reconnaissance spectroscopy and radial velocity (RV) measurements obtained using three separate telescope and spectrograph combinations. The spectroscopic synthesis package SME has been used to derive the stellar photospheric parameters that were used as input to various stellar evolutionary tracks in order to derive the parameters of the system. The planetary transit was also validated to occur on the assumed host star through adaptive imaging and statistical analysis. The star is found to be located in the background of the Hyades cluster at a distance at least 4 times further away from Earth than the cluster itself. The spectrum and the space velocities of EPIC 210894022 strongly suggest it to be a member of the thick disk population. We find that the star is a metal poor ([Fe/H]=-0.53+/-0.05 dex) and alpha-rich somewhat evolved solar-like object of spectral type G3 with Teff=5730+/-50 K, logg=4.15+/-0.1 (cgs), radius of 1.3+/-0.1 R_Sun, and mass of 0.88+/-0.02 M_Sun. The RV detection together with the imaging confirms with a high level of significance that the transit signature is caused by a super-Earth orbiting the star EPIC 210894022. We measure a mass of 8.6+/-3.9 M_Earth and a radius of 1.9+/-0.2 R_Earth. A second more massive object with a period longer than about 120 days is indicated by a long term linear acceleration. With an age of > 10 Gyrs this system is one of the oldest where planets is hitherto detected. Further studies of this planetary system is important since it contains information about the planetary formation process during a very early epoch of the history of our Galaxy.

A 2MASS/AllWISE Search for Extremely Red L Dwarfs: The Discovery of Several Likely L Type Members of β Pic, AB Dor, Tuc-Hor, Argus, and the Hyades

Abstract Young brown dwarfs share many properties with directly imaged giant extrasolar planets. They therefore provide unique laboratories for investigating the full range of temperature and mass encompassed by the growing collection of planets discovered outside our Solar System. Furthermore, if they can be tied to a particular group of coeval stars, they also provide vital anchor points for low-mass empirical isochrones. We have developed a novel procedure for identifying such objects based on their unique 2MASS and AllWISE colors. Using our search criteria, we have identified 50 new, late-type L dwarf candidates, 47 of which are spectroscopically confirmed as L dwarfs with follow-up near-infrared spectroscopy. We evaluate the potential membership of these objects in nearby, young moving groups using their proper motions, photometric distance estimates, and spectroscopic indicators of youth, and find seven likely L-type members belonging to the β Pictoris moving group, the AB Doradus moving group, the Tucana-Horologium association, or the Argus association, in addition to several lower probability members. Also found are two late-type (L5 and L6) potential members of the nearby Hyades cluster (WISEA J043642.75+190134.8 and WISEA J044105.56+213001.5).

A new L5 brown dwarf member of the Hyades cluster with chromospheric activity

Our aim is to identify brown dwarf members of the nearby Hyades open star cluster to determine the photometric and spectroscopic properties of brown dwarfs at moderately old ages and extend the knowledge of the substellar mass function of the cluster. We cross-matched the 2MASS and AllWISE public catalogues and measured proper motions to identify low-mass stars and brown dwarf candidates in an area of radius eight degrees around the central region of the Hyades cluster. We identified objects with photometry and proper motions consistent with cluster membership. For the faintest ($J$\,=\,17.2 mag) most promising astrometric and photometric low-mass candidate 2MASS\,J04183483$+$2131275\@, with a membership probability of 94.5\%, we obtained low-resolution (R\,=\,300--1000) and intermediate-resolution (R\,=\,2500) spectroscopy with the 10.4m Gran Telescopio Canarias. From the low-resolution spectra we determined a L5.0$\pm$0.5 spectral type, consistent with the available photometry. In the intermediate dispersion spectrum we detected H$\alpha$ in emission (marginally resolved with a full width half maximum of $\sim$2.8 \AA{}) and determined a $\log ($L$_{\rm{H}\alpha}$/L$_{\rm bol})=-6.0$ dex. From H$\alpha$ we obtained a radial velocity of 38.0$\pm$2.9 km$\cdot$s$^{-1}$, which combined with the proper motion leads to space velocities which are fully consistent with membership in the Hyades cluster.

BORON ABUNDANCES ACROSS THE “Li–Be DIP” IN THE HYADES CLUSTER

Dramatic deficiencies of Li in the mid-F dwarf stars of the Hyades cluster were discovered by Boesgaard & Tripicco. Boesgaard & King discovered corresponding, but smaller, deficiencies in Be in the same narrow temperature region in the Hyades. With the Space Telescope Imaging Spectrograph on the Hubble Space Telescope we investigate B abundances in the Hyades F stars to look for a potential B dip using the B I resonance line at 2496.8 A. The light elements, Li, Be, and B, are destroyed inside stars at increasingly hotter temperatures: 2.5, 3.5, and 5x10^6 K respectively. Consequently, these elements survive to increasingly greater depths in a star and their surface abundances indicate the depth and thoroughness of mixing in the star. We have (re)determined Li abundances/upper limits for 79 Hyades dwarfs, Be for 43 stars, and B in five stars. We find evidence for a small drop in the B abundance across the Li-Be dip. The B abundances for the four stars in the temperature range 6100-6730 K fit the B-Be correlation found previously by Boesgaard et al. Models of rotational mixing produce good agreement with the relative depletions of Be and B in the dip region. We have compared our nLTE B abundances for the three high B stars on either side of the Li-Be dip with those found by Duncan et al. for the two Hyades giants. This confirms the factor of ~10 decline in the B abundance in the Hyades giants as predicted by dilution due to the deepening of the surface convection zone.

NEW PLEIADES ECLIPSING BINARIES AND A HYADES TRANSITING SYSTEM IDENTIFIED BY K2

ABSTRACT We present the discovery in Kepler’s K2 mission observations and our follow-up radial velocity (RV) observations from Keck/HIRES for four eclipsing binary (EB) star systems in the young benchmark Pleiades and Hyades clusters. Based on our modeling results, we announce two new low mass ( M tot < 0.6 M ⊙ ) EBs among Pleiades members (HCG 76 and MHO 9) and we report on two previously known Pleiades binaries that are also found to be EB systems (HII 2407 and HD 23642). We measured the masses of the binary HCG 76 to ≲2.5% precision, and the radii to ≲4.5% precision, which together with the precise effective temperatures yield an independent Pleiades distance of 132 ± 5 pc. We discuss another EB toward the Pleiades that is a possible but unlikely Pleiades cluster member (AK II 465). The two new confirmed Pleiades systems extend the mass range of Pleiades EB components to 0.2–2 M ⊙ . Our initial measurements of the fundamental stellar parameters for the Pleiades EBs are discussed in the context of the current stellar models and the nominal cluster isochrone, finding good agreement with the stellar models of Baraffe et al. at the nominal Pleiades age of 120 Myr. Finally, in the Hyades, we report a new low mass eclipsing system (vA 50) that was concurrently discovered and studied by Mann et al. We confirm that the eclipse is likely caused by a Neptune-sized transiting planet, and with the additional RV constraints presented here we improve the constraint on the maximum mass of the planet to be ≲1.2 M Jup.

ZODIACAL EXOPLANETS IN TIME (ZEIT). I. A NEPTUNE-SIZED PLANET ORBITING AN M4.5 DWARF IN THE HYADES STAR CLUSTER

ABSTRACT Studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. Recent K2 observations of nearby young clusters (10–800 Myr) have facilitated the discovery of such planetary systems. Here we report the discovery of a Neptune-sized planet transiting an M4.5 dwarf (K2-25) in the Hyades cluster (650–800 Myr). The light curve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. We confirm that the planet host is a member of the Hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph Immersion Grating Infrared Spectrometer. This enables us to calculate a distance based on K2-25's kinematics and membership to the Hyades, which in turn provides a stellar radius and mass to ≃5%–10%, better than what is currently possible for most Kepler M dwarfs (12%–20%). We use the derived stellar density as a prior on fitting the K2 transit photometry, which provides weak constraints on eccentricity. Utilizing a combination of adaptive optics imaging and high-resolution spectra, we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits’ planetary origin. K2-25b has a radius ( 3.43 − 0.31 + 0.95 ?> R ⊕) much larger than older Kepler planets with similar orbital periods (3.485 days) and host-star masses (0.29 M ⊙). This suggests that close-in planets lose some of their atmospheres past the first few hundred million years. Additional transiting planets around the Hyades, Pleiades, and Praesepe clusters from K2 will help confirm whether this planet is atypical or representative of other close-in planets of similar age.

Grids of stellar models including second harmonic and colors: solar composition (Z = 0.0172, X = 0.7024)

Grids of stellar evolution are required in many fields of astronomy/astrophysics, such as planet hosting stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models with updated ingredients and recently determined solar abundances is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough (0.01 M⊙) that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00 M⊙. We present results in different forms of tables for easy and general application. The second stellar harmonic, required for analysis of apsidal motion of eclipsing binaries, is also listed. We also construct rotating models to determine the effect of rotation on stellar structure and derive fitting formulae for luminosity, radius and the second harmonic as a function of rotational parameter. We also compute and list colors and bolometric corrections of models required for transformation between theoretical and observational results. The results are tested for the Sun, the Hyades cluster, the slowly rotating chemically peculiar Am stars and eclipsing binaries with apsidal motion. The theoretical and observational results along isochrones are in good agreement. The grids are also applicable to rotating stars provided that equatorial velocity is given.

Where the Wild Young M Dwarfs Are: the SUPERBLINK Proper Motion Survey and a Search for Low-mass Moving Group Candidates

AbstractThe SUPERBLINK survey catalogs all stars brighter than R = 19 mag and with proper motions larger than 40 mas yr−1, down to a declination of −33○. The catalog inevitably includes a significant fraction of the presumed low-mass members of several nearby young moving groups (Beta Pic, AB Dor, Tuc-Hor, Argus), or low-mass escapees from the Hyades and Pleiades clusters. We discuss opportunities and challenges in identifying the missing M dwarf members of these moving groups. While rounding up the majority of the potential M dwarf members of these groups, such samples are significantly affected by co-moving field stars, both young and old, due to the heavy clumping of the local field population in velocity space.