Cluster Parallaxes Research Articles

A 0.9% calibration of the Galactic Cepheid luminosity scale based on Gaia DR3 data of open clusters and Cepheids

We have conducted a search for open clusters in the vicinity of classical Galactic Cepheids based on high-quality astrometry from the third data release (DR3) of the ESA mission Gaia to improve the calibration of the Leavitt law (LL). Our approach requires no prior knowledge of existing clusters, allowing us to both detect new host clusters and cross-check previously reported associations. Our Gold sample consists of 34 Cepheids residing in 28 open clusters, including 27 fundamental mode and seven overtone Cepheids. Three new bona fide cluster Cepheids are reported (V0378 Cen, ST Tau, and GH Lup) and the host cluster identifications for three others (VW Cru, IQ Nor, and SX Vel) are corrected. The fraction of Cepheids occurring in open clusters within 2 kpc of the Sun is fCC,2 kpc = 0.088−0.019+0.029. Nonvariable cluster members allow us to determine cluster parallaxes to ∼7 μas in the range 12.5 < G < 17 mag, where recent studies found that parallax corrections by Lindegren et al. (2021, A&A, 649, A4, L21) are accurate and require no further offset corrections. By comparing Cepheids in MW clusters to Cepheids in the LMC, we confirm these independent results and the adequacy of the L21 corrections for the cluster members in this range. By combining cluster and field Cepheids, we calibrate the LL for several individual photometric passbands, together with reddening-free Wesenheit magnitudes based on Gaia and HST photometry, while solving for the residual offset applicable to Cepheid parallaxes, ΔϖCep. The most direct comparison of our results with the SH0ES distance ladder yields excellent (0.3σ) agreement for both the absolute magnitude of a 10 d solar metallicity Cepheid in the near-IR HST Wesenheit magnitudes, MH,1W = −5.914 ± 0.017 mag, and the residual parallax offset, ΔϖCep = −13 ± 5 μas. Despite the use of a common set of photometry, this is an important cross-check of the recent Hubble constant measurement by Riess et al. (2022a, ApJ, 938, 36) based on independently determined cluster membership and average parallaxes. Using the larger sample of 26 Gold cluster Cepheids and 225 MW Cepheids with recent Gaia DR3 astrometry and photometry, we determine MG,1W = −6.051 ± 0.020 mag in the optical Gaia Wesenheit magnitude at the sample average iron abundance of (⟨[Fe/H]⟩ = 0.069) and ΔϖCep = −22 ± 3 μas. Correcting to solar metallicity yields MG,1W = −6.004 ± 0.019 mag and ΔϖCep = −19 ± 3 μas. These results mark the currently most accurate absolute calibrations of the Cepheid luminosity scale based purely on observations of Milky Way Cepheids, and it is also the most precise determination of the residual Cepheid parallax offset at a significance of 6 − 7σ.

Cluster Cepheids with High Precision Gaia Parallaxes, Low Zero-point Uncertainties, and Hubble Space Telescope Photometry

We present Hubble Space Telescope (HST) photometry of 17 Cepheids in open clusters and their cluster mean parallaxes from Gaia EDR3. These parallaxes are more precise than those from individual Cepheids (G < 8 mag) previously used to measure the Hubble constant because they are derived from an average of >300 stars per cluster. Cluster parallaxes also have smaller systematic uncertainty because their stars lie in the range (G > 13 mag) where the Gaia parallax calibration is the most comprehensive. Cepheid photometry employed in the period–luminosity relation was measured using the same HST instrument (WFC3) and filters (F555W, F814W, F160W) as extragalactic Cepheids in Type Ia supernova hosts. We find no evidence of residual parallax offset in this magnitude range, zp = −3 ± 4 μas, consistent with the results from Lindegren et al. and most studies. The Cepheid luminosity (at P = 10 d and solar metallicity) in the HST near-infrared, Wesenheit magnitude system derived from the cluster sample is mag and −5.890 ± 0.018 mag with or without simultaneous determination of a parallax offset, respectively. These results are similar to measurements from field Cepheids, confirming the accuracy of the Gaia parallaxes over a broad range of magnitudes. The SH0ES distance ladder calibrated only from this sample gives H 0 = 72.9 ± 1.3 and H 0 = 73.3 ± 1.1 km s−1 Mpc−1 with or without offset marginalization; combined with all other anchors we find H 0 = 73.01 ± 0.99 and 73.15 ± 0.97 km s−1 Mpc−1, respectively, a 5% or 7% reduction in the uncertainty in H 0 and a ∼5.3σ Hubble tension relative to Planck+ΛCDM. It appears increasingly difficult to reconcile two of the best-measured cosmic scales, parallaxes from Gaia and the angular size of the acoustic scale of the cosmic microwave background, using the simplest form of ΛCDM to connect the two.

Gaia EDR3 view on galactic globular clusters

ABSTRACT We use the data from Gaia Early Data Release 3 (EDR3) to study the kinematic properties of Milky Way globular clusters. We measure the mean parallaxes and proper motions (PM) for 170 clusters, determine the PM dispersion profiles for more than 100 clusters, uncover rotation signatures in more than 20 objects, and find evidence for radial or tangential PM anisotropy in a dozen richest clusters. At the same time, we use the selection of cluster members to explore the reliability and limitations of the Gaia catalogue itself. We find that the formal uncertainties on parallax and PM are underestimated by $10{-}20{{\ \rm per\ cent}}$ in dense central regions even for stars that pass numerous quality filters. We explore the spatial covariance function of systematic errors, and determine a lower limit on the uncertainty of average parallaxes and PM at the level 0.01 mas and 0.025 mas yr$^{-1}$ , respectively. Finally, a comparison of mean parallaxes of clusters with distances from various literature sources suggests that the parallaxes for stars with $G&amp;gt;13$ (after applying the zero-point correction suggested by Lindegren et al.) are overestimated by $\sim 0.01\pm 0.003$ mas. Despite these caveats, the quality of Gaia astrometry has been significantly improved in EDR3 and provides valuable insights into the properties of star clusters.

The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations

Aims. Classical Cepheids provide the foundation for the empirical extragalactic distance ladder. Milky Way Cepheids are the only stars in this class accessible to trigonometric parallax measurements. However, the parallaxes of Cepheids from the second Gaia data release (GDR2) are affected by systematics because of the absence of chromaticity correction, and occasionally by saturation. Methods. As a proxy for the parallaxes of 36 Galactic Cepheids, we adopt either the GDR2 parallaxes of their spatially resolved companions or the GDR2 parallax of their host open cluster. This novel approach allows us to bypass the systematics on the GDR2 Cepheids parallaxes that is induced by saturation and variability. We adopt a GDR2 parallax zero-point (ZP) of −0.046 mas with an uncertainty of 0.015 mas that covers most of the recent estimates. Results. We present new Galactic calibrations of the Leavitt law in the V, J, H, KS, and Wesenheit WH bands. We compare our results with previous calibrations based on non-Gaia measurements and compute a revised value for the Hubble constant anchored to Milky Way Cepheids. Conclusions. From an initial Hubble constant of 76.18 ± 2.37 km s−1 Mpc−1 based on parallax measurements without Gaia, we derive a revised value by adopting companion and average cluster parallaxes in place of direct Cepheid parallaxes, and we find H0 = 72.8 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 when all Cepheids are considered and H0 = 73.0 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 for fundamental mode pulsators only.

Photometric, kinematic, and variability study in the young open cluster NGC 1960

ABSTRACT We present a comprehensive photometric analysis of a young open cluster NGC 1960 (= M36) along with the long-term variability study of this cluster. Based on the kinematic data of Gaia DR2, the membership probabilities of 3871 stars are ascertained in the cluster field among which 262 stars are found to be cluster members. Considering the kinematic and trigonometric measurements of the cluster members, we estimate a mean cluster parallax of 0.86 ± 0.05 mas and mean proper motions of μRA = −0.143 ± 0.008 mas yr−1 and μDec. = −3.395 ± 0.008 mas yr−1. We obtain basic parameters of the cluster such as E(B − V) = 0.24 ± 0.02 mag, log(Age/yr) = 7.44 ± 0.02, and d = 1.17 ± 0.06 kpc. The mass function slope in the cluster for the stars in the mass range of 0.72–7.32 M⊙ is found to be γ = −1.26 ± 0.19. We find that mass segregation is still taking place in the cluster which is yet to be dynamically relaxed. This work also presents first high-precision variability survey in the central 13 arcmin × 13 arcmin region of the cluster. The V-band photometric data accumulated on 43 nights over a period of more than 3 yr reveals 76 variable stars among which 72 are periodic variables. Among them, 59 are short period (P &amp;lt; 1 d) and 13 are long period (P &amp;gt; 1 d). The variable stars have V magnitudes ranging between 9.1 to 19.4 mag and periods between 41 min and 10.74 d. On the basis of their locations in the H–R diagram, periods, and characteristic light curves, 20 periodic variables belong to the cluster are classified as 2 δ-Scuti, 3 γ-Dor, 2 slowly pulsating B stars, 5 rotational variables, 2 non-pulsating B stars, and 6 as miscellaneous variables.

A Comprehensive Study of 94 Open Clusters Based on the Data from IPHAS, GAIA DR2, and Other Sky Surveys

We determine the color excesses, photometric distances, ages, astrometric parallaxes and proper motions for 94 open clusters in the northern part of the Milky Way. We estimate the color excesses and photometric distances based on the data from IPHAS photometric survey of the northern Galactic plane using individual total-to-selective extinction ratios R_r=A_r/E_(r-i) for each cluster computed via the color-difference method based on IPHAS r, i, and H_alpha-band, 2MASS J, H, and K_s-band, WISE W1-band, and Pan-STARRS i, z, and y-band data. The inferred R_r values vary significantly from cluster to cluster spanning the R_r=3.1--5.2 interval with a mean and standard deviation equal to <R_r>=3.99 and sigma R_r=0.34, respectively. We identified cluster members using (1) absolute proper motions determined from individual-epoch positions of stars retrieved from IPHAS, 2MASS, URAT1, ALLWISE, UCAC5, and Gaia DR1 catalogs and positions of stars on individual Palomar Sky Survey plates reconstructed based on the data provided in USNO-B1.0 catalog and (2) absolute proper motions provided in Gaia DR2 catalog, and computed the average Gaia DR2 trigonometric parallaxes and proper motions of the clusters. The mean formal error of the inferred astrometric parallaxes of clusters is of about 7microarcseconds, however, a comparison of astrometric and photometric parallaxes of our cluster sample implies that Gaia DR2 parallaxes are, on the average, systematically underestimated by 45 +/-9 microarcseconds. This result agrees with estimates obtained by other authors using other objects. At the same time, we find our photometric distance scale to be correct within the quoted errors (the inferred correction factor is equal to unity to within a standard error of 0.025).

TheGaia-ESO Survey: open clusters inGaia-DR1

Context.Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas.Aims.We describe the methodologies that, taking advantage ofGaia-DR1 and theGaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators.Methods.We perform a homogeneous analysis of eight open clusters using theGaia-DR1 TGAS catalogue for bright members and information from theGaia-ESO Survey for fainter stars. Cluster membership probabilities for theGaia-ESO Survey targets are derived based on several spectroscopic tracers. TheGaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis.Results.For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&amp;A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values.Conclusions.The systematic parallax errors inherent in theGaiaDR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combiningGaiaand ground-based spectroscopic datasets.

K2-231 b: A Sub-Neptune Exoplanet Transiting a Solar Twin in Ruprecht 147

Abstract We identify a sub-Neptune exoplanet (R p = 2.5 ± 0.2 ) transiting a solar twin in the Ruprecht 147 star cluster (3 Gyr, 300 pc, [Fe/H] = +0.1 dex). The ∼81 day light curve for EPIC 219800881 (V = 12.71) from K2 Campaign 7 shows six transits with a period of 13.84 days, a depth of ∼0.06%, and a duration of ∼4 hr. Based on our analysis of high-resolution MIKE spectra, broadband optical and NIR photometry, the cluster parallax and interstellar reddening, and isochrone models from PARSEC, Dartmouth, and MIST, we estimate the following properties for the host star: M ⋆ = 1.01 ± 0.03 , R ⋆ = 0.95 ± 0.03 , and = 5695 ± 50 K. This star appears to be single based on our modeling of the photometry, the low radial velocity (RV) variability measured over nearly 10 yr, and Keck/NIRC2 adaptive optics imaging and aperture-masking interferometry. Applying a probabilistic mass–radius relation, we estimate that the mass of this planet is M p = 7 + 5 – 3 , which would cause an RV semi-amplitude of K = 2 ± 1 that may be measurable with existing precise RV facilities. After statistically validating this planet with BLENDER, we now designate it K2-231b, making it the second substellar object to be discovered in Ruprecht 147 and the first planet; it joins the small but growing ranks of 22 other planets and three candidates found in open clusters.

Gaia Data Release 1

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.

An Update on Monitoring Stellar Orbits in the Galactic Center

Abstract Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center, we present an update of the main results from this unique data set: a measurement of mass and distance to Sgr A*. Our progress is not only due to the eight-year increase in time base, but also to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to Sgr A*; the statistical errors of 0.13 × 10 6 M ⊙ and 0.12 kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, the star S1 also yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M = 4.28 ± 0.10 ∣ stat . ± 0.21 ∣ sys × 10 6 M ⊙ and R 0 = 8.32 ± 0.07 ∣ stat . ± 0.14 ∣ sys kpc . These numbers are in agreement with the recent determination of R 0 from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from Sgr A*, and of the radio source Sgr A* agree to within 1 mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars that we can explicitly show are members of the clockwise disk of young stars, and which have lower-eccentricity orbits.

Stellar twins determine the distance of the Pleiades

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 cluster parallax of $7.42\pm0.09~\mathrm{mas}$ corresponding to a mean cluster distance of ${ 134.8\pm 1.7~\mathrm{pc}}$. This value agrees with the current results obtained from stellar evolution models.

A SURVEY FOR A COEVAL, COMOVING GROUP ASSOCIATED WITH HD 141569

We present results of a search for a young stellar moving group associated with the star HD 141569, a nearby, isolated Herbig AeBe primary member of a 5+/-3 Myr-old triple star system on the outskirts of the Sco-Cen complex. Our spectroscopic survey identified a population of 21 Li-rich, <30 Myr-old stars within 30 degrees of HD 141569 which possess similar proper motions with the star. The spatial distribution of these Li-rich stars, however, is not suggestive of a moving group associated with the HD 141569 triplet, but rather this sample appears cospatial with Upper Scorpius and Upper Centaurus Lupus. We apply a modified moving cluster parallax method to compare the kinematics of these youthful stars with Upper Scorpius and Upper Centaurus Lupus. Eight new potential members of Upper Scorpius and five new potential members of Upper Centaurus Lupus are identified. A substantial moving group with an identifiable nucleus within 15 degrees (~30 pc) of HD 141569 is not found in this sample. Evidently, the HD 141569 system formed ~5 Myr ago in relative isolation, tens of parsecs away from the recent sites of star formation in the Ophiucus-Scorpius-Centaurus region.

Nearby Open Clusters and HR Diagram Calibration

13 clusters have been analysed (Coma Ber, the Pleiades, IC 2602, IC 2391, Praesepe, Alpha Per, NGC 6475, Blanco 1, Stock 2, NGC 6633, IC 4756, NGC 2516 and NGC 3532). Cluster members have been selected using Hipparcos proper motions and parallaxes. The mean cluster parallaxes have been determined using Hipparcos intermediate data (abscissae on the Reference Great Circles) taking into account star to star correlations. Both selection of members and computation of cluster mean parallaxes are described in Mermilliod et al., 1997 and Robichon et al., 1997.For each cluster, a selection of fainter stars in the ‘Base des Amas’ (Mermilliod, 1988), based on photometric data as well as radialvelocities and proper motions when available, has been done. From this selection and the computed mean parallaxes, the location of the 13 cluster sequences in the observational HR diagram is derived very accurately, at least for the closest clusters for which good photometry and small errors on the mean parallaxes are available. Relative positions of cluster sequences cannot only be explained by differences between cluster metallicities. For example, the Pleiades sequence is 0.5 magnitude bellow the Praesepe sequence whereas the adopted metallicities (obtained spectroscopically i.e. whithout any assumption on the helium content) are respectively -0.034 and +0.10.

Map-based trigonometric parallaxes of open clusters: Coma

view Abstract Citations (13) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS MAP-based Trigonometric Parallaxes of Open Clusters: Coma Gatewood, George Abstract This is the fourth study in a series to determine the direct trigonometric parallaxes of four of the nearest open star clusters, the Hyades, the Pleiades, the Praesepe, and the nearby cluster in Coma (Gatewood et al. 1990; Gatewood et al. 1992); Gatewood & Kiewiet de Jonge 1994). The results for the open star cluster in Coma are compared with those of the other three clusters, and the members are found to be significantly subluminous. The trigonometric parallax of the cluster is estimated from that of three members studied with the Multichannel Astrometric Photometer (MAP) at the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of the cluster is +13.53 +/- 0.54 mass (0.00054 min), corresponding to a distance modulus of 4.34 +/- 0.09 mag. The U-B excess of the Coma cluster members may be used to adjust the observed absolute magnitudes and the B-V measurements as suggested by Sandage & Eggen (1959). The agreement obtained in this manner suggests that, like subdwarf stars, the stars of the Coma cluster appear subluminous because of line blanketing. One of the three members observed in this study was recognized as a member by its parallax and is the faintest known member of the cluster. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175733 Bibcode: 1995ApJ...445..712G Keywords: Astrography; Astrometry; Open Clusters; Stellar Parallax; Trigonometry; Data Reduction; Distance; Magnitude; Stellar Luminosity; Stellar Motions; Astrophysics full text sources ADS | data products SIMBAD (14) Related Materials (4) Part 1: 1990ApJ...364..114G Part 2: 1992ApJ...392..710G Part 3: 1994ApJ...428..166G Part 5: 2000ApJ...533..938G

Map-based trigonometric parallaxes of open clusters: The Praesepe

view Abstract Citations (17) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Map-based Trigonometric Parallaxes of Open Clusters: The Praesepe Gatewood, George ; de Jonge, Joost Kiewiet Abstract Trigonometric parallaxes for stars in the Praesepe open star cluster are deduced from data collected with the Multichannel Astrometric Photometer (MAP) at the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of five cluster members is +5.21 +/- 0.79 mas (0.00079 arcsec), corresponding to a distance modulus of 6.42 +/- 0.33 mag. We briefly compare this result with that derived earlier for the Hyades and note agreement with the distance found by main-sequence fitting. We also discuss briefly an improvement in the weighting scheme of the centroiding algorithm used in this series. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174229 Bibcode: 1994ApJ...428..166G Keywords: Astrometry; Praesepe Star Clusters; Stellar Parallax; Stellar Spectrophotometry; Algorithms; Main Sequence Stars; Weighting Functions; Astronomy; ASTROMETRY full text sources ADS | data products SIMBAD (12) Related Materials (4) Part 1: 1990ApJ...364..114G Part 2: 1992ApJ...392..710G Part 4: 1995ApJ...445..712G Part 5: 2000ApJ...533..938G

The Sirius supercluster in the FK5

view Abstract Citations (35) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Sirius Supercluster in FK5 Eggen, Olin J. Abstract Fifty-five stars in the FK5 or with PPM(H) quality proper motions are discussed as members of the Sirius supercluster. The convergent point of the supercluster motion is (A, D) = (20.55h -38.1 deg) and the space velocity is V(T) = 18.6 + 0.005X km/s, where X is the radial distance of the members from the sun. The member stars indicate (Fe/H) Hyades - (Fe/H) Sirius = 0.18 dex from both photometric and spectroscopic evidence. The bulk of the supercluster members fall into two age groups, 6.3 x 10 exp 8 and 10 exp 9 yr on the basis of models with convective overshoot. The available observations of chromospheric activity in Mg II (h and k) are quantized into three well-defined groups for both Sirius supercluster and Hyades cluster dwarfs. For 20 supercluster members with cluster parallax greater than 0.03 arcsec the ratio of pi(cluster)/pi(trigonometric) = 0.95 +/- 0.20(sigma). Publication: The Astronomical Journal Pub Date: October 1992 DOI: 10.1086/116334 Bibcode: 1992AJ....104.1493E Keywords: Chronology; Star Clusters; Stellar Motions; Stellar Spectrophotometry; A Stars; Binary Stars; Chromosphere; Dwarf Stars; Radial Velocity; Astrophysics; GALAXIES: STAR CLUSTERS full text sources ADS | data products SIMBAD (97)

Map-based trigonometric parallaxes of open clusters. II - The Hyades: 51 Tauri

The trigonometric parallax, mass, and mass ratio of 51 Tauri, a binary member of the Hyades star cluster, are determined. The parallax solution, 19.4 mas with a standard error of 1.1 mas, is slightly greater than its generally accepted value and yields a cluster distance of 4.30 +/-2.0 pc or a distance modulus equivalent of 3.16 +/- 0.10 mag, in excellent agreement with recent photographic parallax results. The weighted mean of all trigonometric parallax determinations of the cluster is now 22.9 +/-0.6 mas or a modulus of 3.20 +/- 0.06 mag. The total mass of the 51 Tauri system was found to be 2.56 +/- 0.44 solar masses. Adopting a magnitude difference in line with the spectral types of the components yields individual masses of 1.61 +/- 0.28 and 0.95 +/- 0.18 solar masses. This result places the mass of both the A8 V primary and the G0 secondary stars within the errors of the measurement of the mass-luminosity relation established for solar-neighborhood main-sequence stars.

The Pleiades supercluster in FK 5

view Abstract Citations (35) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Pleiades Supercluster in FK 5 Eggen, Olin J. Abstract The age distribution of the early-type supercluster members which dominate FK 5 is studied by means of the proper motions derived by Fricke et al. (1988). The main values of the total space velocity of the members and their dependence on radial distance from the sun demonstrates the characteristic dependence of isoperiodic galactic orbits. Models incorporating convective overshoot yield a wide range of ages, and dual epochs of star formation are identified for some individual clusters. The results of the analysis include three wide pairs of premain-sequence stars, three late-type supergiants, and one evolved close visual binary. Recent speckle observations can be utilized to determine the orbit of the latter binary and to determine the structure of a potential equal-component binary comprising two main-sequence stars. Orbital and stellar parameters are listed for the clusters which make up the Pleiades supercluster including periods, cluster parallaxes, and individual masses. Publication: The Astronomical Journal Pub Date: April 1992 DOI: 10.1086/116142 Bibcode: 1992AJ....103.1302E Keywords: Astronomical Catalogs; Binary Stars; Pre-Main Sequence Stars; Star Clusters; Supergiant Stars; Main Sequence Stars; Stellar Evolution; Astrophysics; LOCAL GROUP; GALAXIES: CLUSTERING; GALAXIES: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (51)

Map-based trigonometric parallaxes of open clusters - The Pleiades

The multichannel astrometric photometer and Thaw refractor of the University of Pittsburgh's Allegheny Observatory have been used to determine the trigonometric parallax of the Pleiades star cluster. The distance determined, 150 with a standard error of 18 parsecs, places the cluster slightly farther away than generally accepted. This suggests that the basis of many estimations of the cosmic distance scale is approximately 20 percent short. The accuracy of the determination is limited by the number and choice of reference stars. With careful attention to the selection of reference stars in several Pleiades regions, it should be possible to examine differences in the photometric and trigonometric modulus at a precision of 0.1 magnitudes.

The Search for Unwanted Signals: Systematic Trends in Proper Motions of Fundamental Stars

An investigation of the N30 along the same lines as that of the FK4 (Brosche and Schwan 1981) reveals quite similar non-standard systematic motions. Some consequences are indicated for the determination of cluster parallaxes, of secular parallaxes and of the galactic rotation. In general, we stress the necessity of always searching for every signal in the data - including those ones which are not understood and hence not ‘wanted’.