Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/695/1527
- Title:
- HR 8257: orbit and basic properties
- Short Name:
- J/ApJ/695/1527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used interferometric and spectroscopic observations of HR 8257 to determine a three-dimensional orbit of the system. The orbit has a period of 12.21345 days and an eccentricity of 0.2895. The masses of the F0 and F2 dwarf components are 1.56 and 1.38M_{sun}_, respectively, with fractional errors of 1.4%. Our orbital parallax of 13.632+/-0.095mas, corresponding to a distance of 73.4+/-0.6pc, differs from the Hipparcos result by just 2% and has a significantly smaller uncertainty. From our spectroscopic observations and spectral energy distribution modeling we determine the component effective temperatures and luminosities to be T_eff_(A)=7030+/-200K and T_eff_(B)=6560+/-200K and L_A_=9.4+/-0.3L_{sun}_ and L_B_=4.7+/-0.2L_{sun}_. The primary rotates pseudosynchronously, while the secondary is not far from its pseudosynchronous rotational velocity. Although both early-F stars are slowly rotating, neither component of this close binary is an Am star. A comparison with evolutionary tracks indicates that the stars are slightly metal poor, and although the components have evolved away from the zero-age main sequence, they are both still dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/152
- Title:
- HST FGS-1r parallaxes for 8 metal-poor stars
- Short Name:
- J/ApJ/835/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H]< -1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144{mu}as. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02-0.03 mag. Six of these stars are on the main sequence (MS) (with -2.7<[Fe/H]< -1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O'Malley+ (2017ApJ...838...90O), we find that standard stellar models using the VandenBerg & Clem (2003AJ....126..778V) color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H]=-2.5) being anomalous in its location in the color-magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with -2.4{<=}[Fe/H]{<=}-1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7+/-1.0Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/106/637
- Title:
- ICCD speckle observations. IX
- Short Name:
- J/AJ/106/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiplicity of stars within clusters is a well-studied phenomenon. However, recent survey work done on the Hyades by Mason et al. [1993AJ....105..220M] would seem to indicate that even in the most often studied clusters, there may be binaries yet undiscovered. In order to expand the sample of cluster binaries with potentially short-period visual orbits, a speckle survey of 45 Pleiades, 54 Praesepe, and 22 IC 4665 bright stars (V < 10) for possible multiplicity was conducted at the KPNO 4 m Mayall telescope between 1987 October and 1991 November. Of these, three new binaries have been discovered: one in the Pleiades where the new component may be spectroscopic, another in Praesepe which has been confirmed from examinations of archival observations and also has been resolved by occultation, and the third in IC 4665. Continued study of these new binary stars could further refine the cluster distance moduli as well as the cluster mass-luminosity relations.
- ID:
- ivo://CDS.VizieR/J/AJ/108/2299
- Title:
- ICCD speckle observations of binary stars. XI.
- Short Name:
- J/AJ/108/2299
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One-thousand one-hundred ninety-seven observations of 730 binary star systems, observed by means of speckle interferometry with the 4m telescope on Kitt Peak, are presented. Included in these binary stars are new interferometric companions to five visual binaries. These measurements, made mostly during the period 1991 to 1993, comprise the 11th installment of results stemming from our speckle program at the 4m class telescopes on Kitt Peak, Cerro Tololo, and Mauna Kea.
- ID:
- ivo://CDS.VizieR/J/AJ/111/936
- Title:
- ICCD Speckle obs. of binary stars. XIII
- Short Name:
- J/AJ/111/936
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Nine hundred eighty-nine observations of 694 binary star systems, observed by means of speckle interferometry with the 4m telescope on Cerro Tololo, are presented. Included in these observations are three new interferometric binaries and new interferometric companions to four visual binaries. These measurements, made during the period 1989-1994, comprise the 13th installment of digital results stemming from our speckle program at several major observatories, and the 23rd list since the program's inception in 1975.
- ID:
- ivo://CDS.VizieR/J/AJ/119/3084
- Title:
- ICCD speckle obs. of binary stars. XXIII.
- Short Name:
- J/AJ/119/3084
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 2017 observations of 1286 binary stars, observed by means of speckle interferometry using six telescopes over a 15 year period from 1982 April to 1997 June. These measurements constitute the 23d installment in CHARA's speckle program at 2 to 4 m class telescopes and include the second major collection of measurements from the Mount Wilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are also presented for 14 systems, seven of which have had no previously published orbital analyses.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A132
- Title:
- IK Tau and HIP 20188 visible polarimetric imaging
- Short Name:
- J/A+A/628/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present visible polarimetric imaging observations of the oxygen-rich AGB star IK Tau obtained with SPHERE-ZIMPOL (phase 0.27) as well as interferometric observations with AMBER. The polarimetric imaging capabilities of SPHERE-ZIMPOL have allowed us to spatially resolve clumpy dust clouds at 20-50mas from the central star, which corresponds to 2-5R* when combined with a central star's angular diameter of 20.7+/-1.53 mas measured with AMBER. The diffuse, asymmetric dust emission extends out to ~73R*. We find that the TiO emission extends to 150 mas (15R*). The AMBER data in the CO lines also suggest a molecular outer atmosphere extending to ~1.5R*. The results of our 2-D Monte Carlo radiative transfer modelling of dust clumps suggest that the polarized intensity and degree of linear polarization can be reasonably explained by small-sized (0.1{mu}m) grains of Al_2_O_3, MgSiO_3, or Mg_2_SiO_4 in an optically thin shell ({tau}_550 nm=0.5+/-0.1) with an inner boundary radius of 3.5*. IK Tau's mass-loss rate is 20 to 50 times higher than the previously studied AGB stars W Hya, R Dor, and o Cet. Nevertheless, our observations of IK Tau revealed that clumpy dust formation occurs close to the star as seen in those low mass-rate AGB stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/445/845
- Title:
- Implications of the Galactic aberration for CRF
- Short Name:
- J/MNRAS/445/845
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the last few years, much attention has been paid to the astrometric implications of the galactic aberration in proper motions (GA). This effect causes systematic errors in astrometric measurements at a {mu}as level. Some authors consider it so serious that it requires redefinition of the Celestial Reference Frame (CRF). We argue that such attention to the GA is exaggerated too much. It is just a small astrometric correction that must be taken into account during highly accurate astrometric and geodetic data processing. The accuracy of this correction depends on the accuracy of the Galactic rotation parameters and, for most applications, on the accuracy of the rotation matrix between Galactic and equatorial systems. Our analysis has shown that our current knowledge of these two factors is sufficient to compute the correction of the GA with an accuracy better than 10 per cent. The remaining effect at the level of a few tenths {mu}as/yr is negligible nowadays. Another consequence of introducing the GA correction is the necessity to return to classical astrometric modelling of the extragalactic radio source position - derived by very-long-baseline interferometry (VLBI) - by the linear trend model. Changing the current paradigm of the VLBI-derived CRF, based on the assumption of zero motion of radio sources, to classical one leads to bias in the radio source positions of up to several tens of {mu}as for a catalogue at epoch J2000.0.
