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We present 1103 trigonometric parallaxes and proper motions from the United States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT) observations taken at the Naval Observatory Flagstaff Station (NOFS) over a 3 year period from April 2012 to June 2015 covering the entire sky north of about minus 10 deg declination. We selected 2 samples previously suspected nearby stars from known photometric distances and stars showing a large, significant parallax signature in URAT epoch data without any prior selection criteria. All systems presented in this paper have an observed parallax greater than equal to 40 mas with no previous published trigonometric parallax. The formal errors on these weighted parallax solutions are mostly between 4 and 10 mas. This sample gives a significant (order 50%) increase to the number of known systems having a trigonometric parallax to be within 25 pc of the Sun (without applying Lutz Kelker bias corrections). A few of these are found to be within 10 pc. Many of these new nearby stars display a total proper motion of less than 200 mas per year. URAT parallax results have been verified against Hipparcos and Yale data for stars in common. The publication of all significant parallax observations from URAT data is in preparation for CDS.
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We present 916 trigonometric parallaxes and proper motions of newly discovered nearby stars from the United States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT). Observations were taken at the Cerro Tololo Interamerican Observatory (CTIO) over a 2 year period from Oct 2015 to Oct 2017 covering the entire sky south of about +25 deg declination. SPM4 and UCAC4 early epoch catalog data were added to extend the temporal coverage for the parallax and proper motion fit up to 48 years. Using these new URAT parallaxes, optical and near-IR photometry from the APASS and 2MASS catalogs, we identify possible new nearby dwarfs, young stars, low-metallicity subdwarfs and white dwarfs. Comparison to known trigonometric parallaxes show a high quality of the URAT-based results confirming the error in parallax of the URAT south parallaxes reported here to be between 2 and 13 mas. We also include additional 729 trigonometric parallaxes from the URAT north 25 pc sample published in Finch & Zacharias (2016) here after applying the same criterion as for the southern sample to have a complete URAT 25 pc sample presented in this paper.
The URAT Parallax Catalog (UPC) consists of 112,177 parallaxes. The catalog utilizes all Northern Hemisphere exposures from the United States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT) obtained between April 2012 and June 2015. Relative parallaxes are converted to absolute using photometric distance estimates of UCAC4 reference stars. There are 2 groups of stars in this catalog: 1) 58,677 stars with prior published trigonometric parallax (Hipparcos, Yale Parallax Catalog, MEarth project and SIMBAD), and 2) 53,500 stars with first time trigonometric parallaxes as obtained from URAT data. More stringent selection criteria have been applied for group 2 then for group 1 in order to keep the rate of false detections low. The mean error in UPC parallaxes is 10.8 and 4.3 mas for groups 1 and 2, respectively. All stars in UPC are north of -13 deg Dec and between 6.5 and 17 mag. The UPC is published by CDS as catalog I/333 and the acronym has been registered with the IAU. The Finch & Zacharias (2016, in press with AJ) paper describes the data, reductions, and results of an about 1000 star subset (stars within 40 pc of the Sun) of the entire UPC. The UPC also provides accurate positions and proper motions on the ICRS. This is the largest parallax catalog published since the Hipparcos Catalog.
The second data release of it Gaia rm revealed a parallax zero point offset of $-0.029$~mas based on quasars. The value depended on the position on the sky, and also likely on magnitude and colour. The offset and its dependence on other parameters inhibited an improvement in the local distance scale using e.g. the Cepheid and RR Lyrae period-luminosity relations. Analysis of the recent it Gaia rm Early Data Release 3 (EDR3) reveals a mean parallax zero point offset of $-0.021$~mas based on quasars. The it Gaia rm team addresses the parallax zero point offset in detail and proposes a recipe to correct for it, based on ecliptic latitude, $G$-band magnitude, and colour information. This paper is a completely independent investigation into this issue focussing on the spatial dependence of the correction based on quasars and the magnitude dependence based on wide binaries. The spatial and magnitude corrections are connected to each other in the overlap region between $17 < G < 19$. The spatial correction is presented at several spatial resolutions based on the HEALPix formalism. The colour dependence of the parallax offset is unclear and in any case secondary to the spatial and magnitude dependence. The spatial and magnitude corrections are applied to two samples of brighter sources, namely a sample of $sim$100 stars with independent trigonometric parallax measurements from it HST rm data, and a sample of 75 classical cepheids using photometric parallaxes. The mean offset between the observed GEDR3 parallax and the independent trigonometric parallax (excluding outliers) is about $-39$~muas, and after applying the correction it is consistent with being zero. For the classical cepheid sample it is suggested that the photometric parallaxes may be underestimated by about 5%.
We have conducted a 4030-square-deg near-infrared proper motion survey using multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778 proper motion candidates, 647 of which are not listed in SIMBAD. After comparison to DSS images, we find that 107 of our proper motion candidates lack counterparts at B-, R-, and I-bands and are thus 2MASS-only detections. We present results of spectroscopic follow-up of 188 targets that include the infrared-only sources along with selected optical-counterpart sources with faint reduced proper motions or interesting colors. We also establish a set of near-infrared spectroscopic standards with which to anchor near-infrared classifications for our objects. Among the discoveries are six young field brown dwarfs, five red L dwarfs, three L-type subdwarfs, twelve M-type subdwarfs, eight blue L dwarfs, and several T dwarfs. We further refine the definitions of these exotic classes to aid future identification of similar objects. We examine their kinematics and find that both the blue L and red L dwarfs appear to be drawn from a relatively old population. This survey provides a glimpse of the kinds of research that will be possible through time-domain infrared projects such as the UKIDSS Large Area Survey, various VISTA surveys, and WISE, and also through z- or y-band enabled, multi-epoch surveys such as Pan-STARRS and LSST.
Westerlund 1 (Wd1) is potentially the largest star cluster in the Galaxy. That designation critically depends upon the distance to the cluster, yet the cluster is highly obscured, making luminosity-based distance estimates difficult. Using {it Gaia} Data Release 2 (DR2) parallaxes and Bayesian inference, we infer a parallax of $0.35^{+0.07}_{-0.06}$ mas corresponding to a distance of $2.6^{+0.6}_{-0.4}$ kpc. To leverage the combined statistics of all stars in the direction of Wd1, we derive the Bayesian model for a cluster of stars hidden among Galactic field stars; this model includes the parallax zero-point. Previous estimates for the distance to Wd1 ranged from 1.0 to 5.5 kpc, although values around 5 kpc have usually been adopted. The {it Gaia} DR2 parallaxes reduce the uncertainty from a factor of 3 to 18% and rules out the most often quoted value of 5 kpc with 99% confidence. This new distance allows for more accurate mass and age determinations for the stars in Wd1. For example, the previously inferred initial mass at the main-sequence turn-off was around 40 M$_{odot}$; the new {it Gaia} DR2 distance shifts this down to about 22 M$_{odot}$. This has important implications for our understanding of the late stages of stellar evolution, including the initial mass of the magnetar and the LBV in Wd1. Similarly, the new distance suggests that the total cluster mass is about four times lower than previously calculated.
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