scholarly journals New nearby white dwarfs from Gaia DR1 TGAS and UCAC5/URAT

2018 ◽  
Vol 613 ◽  
pp. A26 ◽  
Author(s):  
R.-D. Scholz ◽  
H. Meusinger ◽  
H. Jahreiß
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Orbital Motion ◽  
Angular Separation ◽  
Proper Motions ◽  
Halo Star ◽  
Physical Separation ◽  
Naval Observatory ◽  
Nearby Stars ◽  
Absolute Magnitudes

Aims. Using an accurate Tycho-Gaia Astrometric Solution (TGAS) 25 pc sample that is nearly complete for GK stars and selecting common proper motion (CPM) candidates from the 5th United States Naval Observatory CCD Astrograph Catalog (UCAC5), we search for new white dwarf (WD) companions around nearby stars with relatively small proper motions. Methods. To investigate known CPM systems in TGAS and to select CPM candidates in TGAS+UCAC5, we took into account the expected effect of orbital motion on the proper motion and proper motion catalogue errors. Colour-magnitude diagrams (CMDs) MJ ∕J − Ks and MG ∕G − J were used to verify CPM candidates from UCAC5. Assuming their common distance with a given TGAS star, we searched for candidates that occupied similar regions in the CMDs as the few known nearby WDs (four in TGAS) and WD companions (three in TGAS+UCAC5). The CPM candidates with colours and absolute magnitudes corresponding neither to the main sequence nor to the WD sequence were considered as doubtful or subdwarf candidates. Results. With a minimum proper motion of 60 mas yr−1, we selected three WD companion candidates; two of which are also confirmed by their significant parallaxes measured in URAT data, whereas the third may also be a chance alignment of a distant halo star with a nearby TGAS star that has an angular separation of about 465 arcsec. One additional nearby WD candidate was found from its URAT parallax and GJKs photometry. With HD 166435 B orbiting a well-known G1 star at ≈24.6 pc with a projected physical separation of ≈700 AU, we discovered one of the hottest WDs, classified by us as DA2.0 ± 0.2, in the solar neighbourhood. We also found TYC 3980-1081-1 B, a strong cool WD companion candidate around a recently identified new solar neighbour with a TGAS parallax corresponding to a distance of ≈8.3 pc and our photometric classification as ≈M2 dwarf. This raises the question of whether previous assumptions on the completeness of the WD sample to a distance of 13 pc were correct.

Blended Visual Binaries as Tests of Low Amplitude Orbit Detection and Determination Capability in Long-Focus Photographic Astrometry

1983 ◽  
Vol 62 ◽  
pp. 45-51
Author(s):  
Sarah Lee Lippincott ◽  
John L. Hershey
Keyword(s):  
Main Sequence ◽  
Orbital Motion ◽  
Orbital Elements ◽  
Detection Capability ◽  
Single Star ◽  
Planetary Mass ◽  
Residual Series ◽  
Nearby Stars ◽  
Low Amplitude ◽  
Visual Binaries

AbstractPhotocentric orbital motions from 60-year Sproul plate series are shown for three visual binaries, ζ Her, 85 Peg and Ho 296. Mass ratios of the first two pairs, which have large-amplitude blended orbits, carry internal errors at the level of one percent. Orbital elements computed independently from the blended photographic observations agree closely with the well-determined visual orbits. Ho 296 serves as a test of the Sproul plate series to detect a 20-year orbit with an amplitude of two, or one, micron. Simulations of orbital motion in single star residual series confirm this detection capability, which corresponds to planetary mass for dark objects around nearby stars. A mass-luminosity diagram of the lower main sequence is shown, including one for invisible astrometric companions.

scholarly journals On Inconsistencies Found in Long-Term Parallax Series

1974 ◽  
Vol 61 ◽  
pp. 317-317
Author(s):  
W. D. Heintz
Keyword(s):  
Proper Motion ◽  
Orbital Motion ◽  
Proper Motions ◽  
Great Caution

Two recent papers (Hershey; Gatewood and Eichhorn; Astron. J., 1973) pointed out that:(1) A proper motion irregularity interpreted as orbital motion was found duplicated in another field.(2) The discontinuity found at one telescope failed to be confirmed by others, and might be ascribed to mere instrumental errors.After the duplication was discovered two years ago, further measurements have revealed an identical pattern in at least seven parallax stars. Yet the cause of the effect, and the reason for its absence in other cases, have not been located. Colour effects and filter problems appear to be ruled out. Indications for discontinuities occurring at other epochs were found. Thus, the question cannot yet be safely answered whether the small variations (one or two micron) of proper motions reported in some cases are spurious; in any case, great caution should be exercised in interpreting one-micron effects unless confirmation from another instrument is obtained.

scholarly journals TESS observations of pulsating subdwarf B stars: extraordinarily short-period gravity modes in CD−28° 1974

2020 ◽  
Vol 493 (4) ◽  
pp. 5162-5169 ◽  
Author(s):  
M D Reed ◽  
K A Shoaf ◽  
P Németh ◽  
J Vos ◽  
M Uzundag ◽  
...  
Keyword(s):  
Main Sequence ◽  
Orbital Motion ◽  
Proper Motions ◽  
Reflection Effect ◽  
Echelle Spectrograph ◽  
Single Star ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Short Period ◽  
Typical Period

ABSTRACT Transiting Exoplanet Survey Satellite (TESS) observations show CD−28° 1974 to be a gravity(g)-mode-dominated hybrid pulsating subdwarf B (sdBV) star. It shows 13 secure periods that form an ℓ = 1 asymptotic sequence near the typical period spacing. Extraordinarily, these periods lie between 1500 and 3300 s, whereas typical $\ell = 1\, g$ modes in sdBV stars occur between 3300 and 10 000 s. This indicates a structure somewhat different from typical sdBV stars. CD−28° 1974 has a visually close F/G main-sequence companion 1.33 arcsec away, which may be a physical companion. Gaia proper motions indicate a comoving pair with the same distance. A reanalysis of Ultraviolet and Visual Echelle Spectrograph (UVES) spectra failed to detect any orbital motion and the light curve shows no reflection effect or ellipsoidal variability, making an unseen close companion unlikely. The implication is that CD−28° 1974 has become a hot subdwarf via single star or post-merger evolution.

scholarly journals Infrared Speckle Interferometry: A Sensitive Technique for Physical Measurements of Unseen Companions to Nearby Stars

1986 ◽  
Vol 109 ◽  
pp. 309-319
Author(s):  
D. W. McCarthy
Keyword(s):  
Main Sequence ◽  
Position Angle ◽  
Speckle Interferometry ◽  
Resolving Power ◽  
Detector Arrays ◽  
Physical Measurements ◽  
Nearby Stars ◽  
Absolute Magnitudes ◽  
Large Telescopes ◽  
Atmospheric Seeing

Infrared speckle interferometry combines the full resolving power of large telescopes with high photometric sensitivity over the wavelength range 2.2 to 12 microns. Despite improved atmospheric seeing at these wavelengths, seeing fluctuations limit measurement precision. Astrometric companions have been detected with angular separations ≥0.1 arcsec and magnitude differences ≤3.7 mag. Results illustrate seeing limitations and show how the usual position angle ambiguity can be overcome. These measurements yield masses and absolute magnitudes for calibrating the lower main sequence. In some cases, orbital motion is detected. A method of “shift-and-add” enables detection of substellar (0.04 to 0.08 M⊙) companions. Future improvements involving detector arrays and seeing monitors are discussed.

scholarly journals On the Correction to Precession from Proper Motions Referred to Galaxies

1971 ◽  
Vol 9 ◽  
pp. 163-170 ◽  
Author(s):  
S. Vasilevskis ◽  
A. R. Klemola
Keyword(s):  
Proper Motion ◽  
Direct Relationship ◽  
Fundamental System ◽  
Direct Reference ◽  
Meridian Circle ◽  
Proper Motions ◽  
Obvious Advantage ◽  
Naval Observatory ◽  
Cooperative Project ◽  
The U.S

One of the principal aims of the Lick proper motion program, as conceived and initiated by Wright (1950), was to derive the correction to precession. Ideally, proper motions of stars from a fundamental catalogue should be measured with respect to galaxies. Unfortunately, these stars are too bright for a direct reference to faint galaxies, even with an objective grating and two systems of exposures (2 h and 1 min) on every plate, as employed at Lick. For this reason a cooperative project with the U.S. Naval Observatory was initiated in 1953 (Scott, 1954; Vasilevskis, 1954), with an intention to establish a direct relationship between meridian circle and Lick observations. When Heckmann (1954) proposed the formation of the AGK3, it was agreed to discontinue the cooperation mentioned, so as to make the resources of the U.S. Naval Observatory available for observing the AGK3 reference stars, and then to use the AGK3 as an intermediary for relating the Lick proper motions to a fundamental system. An obvious advantage of this change was offered by the abundance of AGK stars for measurement on Lick plates; a disadvantage is the absence of the AGK3 data south of declination –2.°5.

scholarly journals Proper Motions in the Bulge: Looking Through Plaut's Low Extinction Window

1998 ◽  
Vol 179 ◽  
pp. 223-224
Author(s):  
R.A. Méndez ◽  
R.M. Rich ◽  
W.F. Van Altena ◽  
T.M. Girard ◽  
S. Van Den Bergh ◽  
...  
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Proper Motions ◽  
Galactic Bulge ◽  
Plate Material

We are conducting the deepest and largest photographic proper-motion survey ever undertaken of the Galactic bulge. Our first-epoch plate material (from 1972-3) goes deep enough (Vlim ∼ 22) to reach below the bulge main-sequence turnoff. These plates cover an area of approximately 25′ × 25′ of the bulge in the low-extinction (Av ∼ 0.8 mag) Plaut field at l= 0°, b= −8°, approximately 1 kpc south of the nucleus. This is the point at which the transition between bulge and halo populations likely occurs and is, therefore, an excellent location to study the interface between the dense metal-rich bulge and the metal-poor halo.

scholarly journals The Variable Shell Star HR 5999

1977 ◽  
Vol 42 ◽  
pp. 137-143
Author(s):  
P.S. Thé ◽  
H.R.E. Tjin A Djie
Keyword(s):  
Spectral Type ◽  
Proper Motion ◽  
Main Sequence ◽  
Angular Separation ◽  
Double Star ◽  
Star System ◽  
Spectroscopic Observations ◽  
Photometric Observations ◽  
Shell Star ◽  
Hydrogen Lines

From spectroscopic observations Bessell and Eggen (1972) (hereafter called BE) have detected that HR 5999 (erroneously named HR 6000 by BE) is a shell star of spectral type A7 III-IV with hydrogen lines in emission. Photometric observations show subsequently that HR 5999 varies in brightness up to about 1 mag semiregularly with a period of about 1 month. Eggen (1975) believes that HR 5999 forms a pre-main sequence object.With HR 6000, the star HR 5999 forms a visual double star system named Δ199; HR 5999 is the southern component. The angular separation is about 45”. BE show that these stars have a common proper motion, and are, therefore, believed to form a physical pair.

scholarly journals Variations in External Parallax Errors

1986 ◽  
Vol 109 ◽  
pp. 247-251
Author(s):  
A. R. Upgren
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Space Velocity ◽  
Proper Motions ◽  
Motion Data ◽  
Hyades Cluster ◽  
High Space ◽  
The Individual ◽  
Van Vleck ◽  
High Space Velocity

The present astrometric program of the Van Vleck Observatory began in 1967. Since then it has emphasized parallaxes and proper motions of stars of the lower main sequence which are not identified on the basis of proper motion and are therefore not biased towards high space velocity. Later an analysis was made from parallax and proper motion data from 70 stars in the spectral range dK3-M2 (Upgren 1973) which found the average external mean error in parallax to be 8.0 ± 1.7 mas (milliarcseconds). This external error was found to vary little from one parallax to another and to have no correlation with the formal internal errors for the individual parallax determinations. Hanson and Lutz (1983) confirm this result using the parallaxes of 14 members of the Hyades cluster also determined at Van Vleck. They find a mean external parallax error of 9.4 ± 1.8 mas and suggest that the proximity of the two determinations may be evidence that Van Vleck parallaxes may be characterized by a single external error. Their slightly larger figure may or may not reflect the relatively fewer plates and epochs of observation from which the Hyades parallaxes were determined.

scholarly journals New ultracool dwarf neighbours within 20 pc from Gaia DR2

2020 ◽  
Vol 637 ◽  
pp. A45
Author(s):  
R.-D. Scholz
Keyword(s):  
Proper Motion ◽  
Visual Inspection ◽  
Near Infrared ◽  
Galactic Plane ◽  
Proper Motions ◽  
Magnitude Diagram ◽  
Motion Measurements ◽  
Moving Groups ◽  
Absolute Magnitudes ◽  
Gaia Dr2

Aims. The Gaia data release 2 (DR2) contains > 6000 objects with parallaxes (Plx + 3 × e_Plx) > 50 mas, placing them within 20 pc from the Sun. Because the expected numbers based on extrapolating the well-known 10 pc census are much lower, nearby Gaia stars need a quality assessment. The 20 pc sample of white dwarfs (WDs) has been verified and completed with Gaia DR2. We here confirm and complete the 20 pc sample of ultracool dwarfs (UCDs) with spectral types ≳M7 and given Gaia DR2 parallaxes. Methods. Dividing the Gaia DR2 20 pc sample into subsamples of various astrometric and photometric quality, we studied their distribution on the sky, in the MG versus G − RP colour-magnitude diagram (CMD), and as a function of G magnitude and total proper motion. After excluding 139 known WDs and 263 known UCDs from the CMD, we checked all remaining ≈3500 candidates with MG >  14 mag (used to define UCDs in this study) for the correctness of their Gaia DR2 proper motions by visual inspection of finder charts, comparison with proper motion catalogues, and comparison with our own proper motion measurements. For confirmed UCD candidates we estimated spectral types photometrically using Gaia and near-infrared absolute magnitudes and colours. Results. We failed to confirm new WDs, but found 50 new UCD candidates that are not mentioned in three previous studies using Gaia DR2. They have relatively small proper motions and low tangential velocities and are concentrated towards the Galactic plane. Half of them have spectral types in SIMBAD and/or previous non-Gaia distance estimates that placed them already within 20 pc. For 20 of the 50 objects, we estimated photometric spectral types of M6−M6.5, slightly below the classical UCD spectral type limit. However, seven L4.5−L6.5, four L0−L1, five M8.5−M9.5, and three M7−M8 dwarfs can be considered as completely new UCDs discoveries within 20 pc based on Gaia DR2. Four M6.5 and two L4.5 dwarfs have high membership probabilities (64%−99%) in the ARGUS, AB Doradus, or Carina Near young moving groups.

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