Improved orbits are presented for the visual binaries WDS 02366+1227, WDS 02434-6643, WDS 03244-1539, WDS 08507+1800, WDS 09128-6055, WDS 11532-1540, WDS 17375+2419, and WDS 22408-0333. The latest orbits for these binaries were demonstrating a great inconsistency between the systemic mass obtained through Kepler's Third Law and that calculated as a sum of their components' mass through standard mass-luminosity and mass-spectrum relationships. Our improvement allowed us to obtain consistent systemic masses for WDS 02434-6643 and WDS 09128-6055 without a need for changing the Hipparcos parallax. For the remaining 6 pairs, we suggest the use of their dynamical parallax as a reliable distance estimate unless more precise parallax is reported. Astrophysical and dynamical properties of individual objects are discussed.
The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data and the development of a new geometric distance measurement for the cluster. A short Pleiades distance from the Hipparcos parallax predicts a number of stars in the solar neighborhood that are sub-luminous at a given photospheric abundance. We test this hypothesis using spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram. We der…
Precise measurement of the fundamental parameters of stellar systems, including mass and radius, depends critically on how well the stellar distances are known. Astrometry from space provides parallax measurements of unprecented accuracy, from which distances can be derived, initially from the Hipparcos mission, with further refinement of that analysis provided by van Leeuwen in 2007. The publication of the Gaia DR2 catalogue promises a dramatic improvement in the available data. We have recalculated the dynamical masses of a sample of 1 700 close visual binary stars using Gaia DR2 and compare…
A history is given of the discovery between 1914 and 1935 of stars of intermediate luminosity between giants and dwarfs with spectral types between G0 to K3. The Mt Wilson spectroscopists identified about 90 such stars in their 1935 summary paper of spectroscopic absolute magnitudes for 4179 stars. Called "subgiants" by Strömberg, these 90 stars defined the group at the time. The position of the Mt Wilson subgiants in the HR diagram caused difficulties in comparisons of high weight trigonometric parallaxes being measured and with Russell's prevailing evolution proposal, and critics questioned …
Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic obser…
Since the release of the Hipparcos catalog in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15 %. As accurate stellar distances are key to understanding stellar structure and evolution, this dilemma puts the validity of stellar evolution models into question. Using our model-independent method to determine parallaxes based on twin stars, we report individual parallaxes of 15 FGK type stars in the Pleiades in anticipation of the astrometric mission Gaia. These parallaxes give a mean…
Aims: We provide a new distance estimate for the Pleiades based on the moving cluster method, which will be useful to further discuss the so-called Pleiades distance controversy and compare it with the very precise parallaxes from the Gaia space mission. Methods: We apply a refurbished implementation of the convergent point search method to an updated census of Pleiades stars to calculate the convergent point position of the cluster from stellar proper motions. Then, we derive individual parallaxes for 64 cluster members using radial velocities compiled from the literature, and approximate par…
We have detected the tip of the Red Giant Branch (TRGB) in the solar neighborhood using near infrared photometry from the 2MASS and DIRBE catalogs, and revised Hipparcos parallaxes. We confirm that the revised Hipparcos parallaxes are superior to the original ones, and that this improvement is necessary to detect the TRGB. We find a tip absolute magnitude of M_K=-6.85+/-0.03, in agreement with that expected from previous tip measurements of the Large Magellanic Cloud, Small Magellanic Cloud, and Bulge. This represents the first geometric calibration of the TRGB and extends previous calibration…
3350 objects from the Sixth catalog of orbits of visual binary stars (ORB6) are investigated to validate Gaia EDR3 parallaxes and provide mass estimates for the systems. We show that 2/3 of binaries with 0.2 - 0.5 arcsec separation are left without a parallax solution in EDR3. A special attention is paid to 521 pairs with parallax known separately for both components. We find 16 entries that are deemed to be chance alignments of unrelated stars. At once we show examples of high-confidence binary systems with significant differences in the reported parallaxes of their components. Next we conclu…
We present the results of a 5.5-year CCD photometric campaign that monitored 261 bright, southern, semi-regular variables with relatively precise Hipparcos parallaxes. The data are supplemented with independent photoelectric observations of 34 of the brightest stars, including 11 that were not part of the CCD survey, and a previously unpublished long time-series of VZ Cam. Pulsation periods and amplitudes are established for 247 of these stars, the majority of which have not been determined before. All M giants with sufficient observations for period determination are found to be variable, wit…
Orbits of 55 visual binary stars are computed using recent speckle interferometry data from the SOAR telescope: 33 first-time orbits and 22 revisions of previous orbit calculations. The orbital periods range from 1.4 to 370 years, the quality of orbits ranges from definitive to preliminary and tentative. Most binaries consist of low-mass dwarfs and have short periods (median period 31 years). The dynamical parallaxes and masses are evaluated and compared to the Hipparcos parallaxes. Using differential speckle photometry, binary components are placed on the color-magnitude diagram.
Polaris, the nearest and brightest Cepheid, is a potential anchor point for the Leavitt period-luminosity relation. However, its distance is a matter of contention, with recent advocacy for a parallax of ~10 mas, in contrast with the Hipparcos measurement of 7.54+/-0.11 mas. We report an independent trigonometric parallax determination, using the Fine Guidance Sensors (FGS) on the Hubble Space Telescope. Polaris itself is too bright for FGS, so we measured its 8th-magnitude companion Polaris B, relative to a network of background reference stars. We converted the FGS relative parallax to absol…
We present a new luminosity-colour relation based on trigonometric parallaxes for thin disc main-sequence stars in SDSS photometry. We matched stars from the newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky Catalogue of Point Sources, and applied a series of constraints, i.e. relative parallax errors ($σ_π/π\leq0.05$), metallicity ($-0.30\leq[M/H]\leq0.20$ dex), age ($0\leq t \leq 10$ Gyr) and surface gravity ($\log g>4$), and obtained a sample of thin disc main-sequence stars. Then, we used our previous transformation equations (Bilir et al. 2008a) between SDSS and 2MA…
We present a Bayesian implementation of isochrone fitting in deriving stellar ages and masses, incorporating absolute K magnitude ($\rm M_K$) derived from 2MASS photometry and Gaia DR1 parallax and differentiation between initial bulk metallicity and present day surface metallicity, with allowance for incorporating further constraints (e.g., asteroseismology) when available. As a test, we re-computed stellar ages and masses of $\sim 4000$ stars in the solar neighbourhood from six well-studied literature samples using both Hipparcos and TGAS parallaxes. Our ages are found to be compatible with …
The Gaia Data Release 1 (DR1) sample of white dwarf parallaxes is presented, including 6 directly observed degenerates and 46 white dwarfs in wide binaries. This data set is combined with spectroscopic atmospheric parameters to study the white dwarf mass-radius relationship (MRR). Gaia parallaxes and G magnitudes are used to derive model atmosphere dependent white dwarf radii, which can then be compared to the predictions of a theoretical MRR. We find a good agreement between Gaia DR1 parallaxes, published effective temperatures (Teff) and surface gravities (log g), and theoretical MRRs. As it…
Accurate stellar masses are requested in order to improve our understanding of stellar interiors, but they are still rather rare. Fortunately, the forthcoming Gaia Mission will provide astrometric measurements permitting the derivation of the orbital inclinations of nearby binaries which are also observed as double-lined spectroscopic binaries (SB2s) with ground-based telescopes. A programme of radial velocity (RV) measurements was initiated in 2010 with the Sophie spectrograph of the Haute-Provence observatory in order to derive accurate SB2 orbits for a large set of stars. Therefore, combine…
Results: We found that the (B-V) v.s. (V-S9W) color-color diagram is useful to identify the stars with infrared excess emerged from circumstellar envelopes/disks. Be stars with infrared excess are well separated from other types of stars in this diagram. Whereas (J-L18W) v.s. (S9W-L18W) diagram is a powerful tool to classify several object-types. Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars form distinct sequences in this color-color diagram. Young stellar objects (YSOs), pre-main sequence (PMS) stars, post-AGB stars and planetary nebulae (PNe) have largest mid-infrared colo…
--Results-- We found that the (B-V) v.s. (V-S9W) color-color diagram is useful to identify the stars with infrared excess emerged from circumstellar envelopes/disks. Be stars with infrared excess are well separated from other types of stars in this diagram. Whereas (J-L18W) v.s. (S9W-L18W) diagram is a powerful tool to classify several object-types. Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars form distinct sequences in this color-color diagram. Young stellar objects (YSOs), pre-main sequence (PMS) stars, post-AGB stars and planetary nebulae (PNe) have largest mid-infrared c…
We present 114 trigonometric parallaxes for 107 nearby white dwarf (WD) systems from both the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI) and the U. S. Naval Observatory Flagstaff Station (NOFS) parallax programs. Of these, 76 parallaxes for 69 systems were measured by the CTIOPI program and 38 parallaxes for as many systems were measured by the NOFS program. A total of 50 systems are confirmed to be within the 25 pc horizon of interest. Coupled with a spectroscopic confirmation of a common proper motion companion to a Hipparcos star within 25 pc as well as confirma…
In anticipation of the Gaia astrometric mission, a sample of spectroscopic binaries is being observed since 2010 with the Sophie spectrograph at the Haute--Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 % when combined with Gaia astrometric measurements. In order to validate the masses derived from Gaia, interferometric observations are obtained for three SB2s in our sample with F-K components: HIP 14157, HIP 20601 and HIP …
Like Hipparcos, Gaia is designed to give absolute parallaxes, independent of any astrophysical reference system. And indeed, Gaia's internal zero-point error for parallaxes is likely to be smaller than any individual parallax error. Nevertheless, due in part to mechanical issues of unknown origin, there are many astrophysical questions for which the parallax zero-point error $σ(π_0)$ will be the fundamentally limiting constraint. These include the distance to the Large Magellanic Cloud and the Galactic Center. We show that by using the photometric parallax estimates for RR Lyrae stars (RRL) wi…
We consider the parallaxes of sixteen cataclysmic variables and related objects that are included in the TGAS catalogue, which is part of the Gaia first data release, and compare these with previous parallax measurements. The parallax of the dwarf nova SS Cyg is consistent with the parallax determination made using the VLBI, but with only one of the analyses of the HST Fine Guidance Sensor (FGS) observations of this system. In contrast, the Gaia parallaxes of V603 Aql and RR Pic are broadly consistent, but less precise than the HST/FGS measurements. The Gaia parallaxes of IX Vel, V3885 Sgr, an…
Preparing for the expected wealth of Gaia detections, we consider here a simple algorithm for classifying unresolved astrometric binaries with main-sequence (MS) primary into three classes: binaries with a probable MS secondary, with two possible values for the mass ratio; probable hierarchical triple MS systems with an astrometric secondary as a close binary, with a limited range of mass-ratio values; and binaries with a compact-object secondary, with a minimal value of the mass ratio. This is done by defining a unit-less observational parameter 'Astrometric Mass-Ratio Function' (AMRF), $\mat…
(abridged)Multiple systems for which the astrometric and spectroscopic orbit are known offer the unique possibility of determining the distance to these systems directly without any assumptions. They are therefore ideal objects for a comparison of Gaia data release 3 (GDR3) parallax data, especially since GDR3 presents the results of the non-single star (NSS) analysis that potentially results in improved parallaxes. An sample of 192 orbital parallax determinations for 186 systems is compiled from the literature. The stars are also potentially in wide binary systems, and 37 candidates were foun…
We present orbital elements, orbital parallaxes and individual component masses, for fourteen spatially resolved double-line spectroscopic binaries derived doing a simultaneous fit of their visual orbit and radial velocity curve. This was done by means of a Markov Chain Monte Carlo code developed by our group, which produces posterior distribution functions and error estimates for all the parameters. Of this sample, six systems had high quality previous studies and were included as benchmarks to test our procedures, but even in these cases we could improve the previous orbits by adding recent …
