I/333 URAT Parallax Catalog (UPC) (Finch+, 2016)
The URAT Parallax Catalog (UPC).
Finch C.T., Zacharias N.
=2016yCat.1333....0F 2016yCat.1333....0F
ADC_Keywords: Surveys ; Positional data ; Parallaxes, trigonometric ;
Proper motions
Keywords: parallaxes - solar neighborhood - stars: distances -
stars: statistics - surveys - astrometry - photometry
Description:
The URAT Parallax Catalog (UPC) consists of 112177 parallaxes. The
catalog utilizes all Northern Hemisphere epoch data from the United
States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT).
This data includes all individual exposures from April 2012 to June
2015 giving a larger epoch baseline for determining parallaxes over
the 2-year span of the First USNO Robotic Astrometric Telescope
Catalog (URAT1) (Zacharias et al., 2015, Cat. I/329) published data.
The URAT parallax pipeline is custom code that utilizes routines from
(Jao, C.-W., 2004, PhD thesis Georgia Stat), the JPL DE405 ephemeris
and Green's parallax factor (Green, R.M., 1985, Spherical Astronomy)
for determining parallaxes from a weighted least-squares reduction.
The relative parallaxes have been corrected to absolute by using the
distance color relation described in (Finch et. al, 2014, Cat.
J/AJ/148/119) to determine a mean distance of all UCAC4 reference
stars (R=8-16 mag) used in the astrometric reductions.
Presented here are all significant parallaxes from the URAT Northern
Hemisphere epoch data comprising of 2 groups: a) URAT parallax results
for stars with prior published parallax, and b) first time
trigonometric parallaxes as obtained from URAT data of stars without
prior published parallax. Note, more stringent selection criteria have
been applied to the second group than the first in order to keep the
rate of false detections low. For specific information about the
astrometric reductions please see 'The First U.S. Naval Observatory
Robotic Astrometric Telescope Catalog' published paper (Zacharias et
al., 2015AJ....150..101Z 2015AJ....150..101Z, Cat. I/329).
For complete details regarding the parallax pipeline please see
'Parallax Results From URAT Epoch Data' (Finch and Zacharias, 2016,
AJ, in press).
This catalog gives all positions on the ICRS at Epoch J2014.0; it
covers the magnitude range 6.56 to 16.93 in the URAT band-pass, with
an average parallax precision of 4.3mas for stars having no known
parallax and 10.8mas for stars matched to external parallax sources.
This catalog covers the sky from about North of -12.75°
declination.
This catalog was matched with the Hipparcos catalog, Yale Parallax
Catalog, (Finch & Zacharias, 2016, AJ, in press), MEarth (Dittmann et.
al., 2014ApJ...784..156D 2014ApJ...784..156D) and the SIMBAD database to obtain known
parallax and star names. For stars matched to SIMBAD using the
automated search feature, only the parallaxes are given so no
information on the parallax errors or source for the parallax are
reported for those stars in this catalog. A flag is included to show
which catalog or database the URAT parallax was matched with. Only the
data from the first catalog that was matched is reported here
according to the following priority list. This means for example, if a
star was matched with Hipparcos, that information was used while
possible other catalog data are not listed here.
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# stars flg catalog
--------------------------------------------------------
53500 0 no catalog match
55549 1 Hipparcos
254 2 Yale Parallax Catalog
1041 3 Finch and Zacharias 2016 (UPM NNNN-NNNN)
1431 4 MEarth parallaxes
402 5 SIMBAD Database (w/parallax)
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112177 total number stars in catalog
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Not all parallaxes from the URAT epoch data are included in this
catalog. Only those data meeting the following criteria have been
included. For the epoch data we only used data having a
FWHM≤7.0pixel; amplitude between 500 and 30000ADU; sigma x,y
≤90.0mas; number of observations ≥20 and epoch span≥1.0 years. The
limits imposed on individual image amplitude, image profile width
(FWHM) and position fit errors (sigma) are set to not allow saturated
stars, stars with too few photons or poorly determined positions to be
used in the parallax solution. We present all URAT parallax solutions
having a known parallax from an external data source regardless of the
quality of the solution (srcflg=1-5). This was done for the user to
better understand the limitations for determining parallaxes with the
current URAT epoch data. For the remaining URAT parallaxes without a
match to any published trigonometric parallax (srcflg=0) we only
present a parallax solutions having:
1) a parallax error ≤10mas
2) a parallax error ≤1/4 the relative parallax
3) epoch span ≥1.5 years
4) number of observations used ≥30
5) fit sigma≤1.4 (unit weight)
6) average image elongation <1.1.
All of these cuts have been implemented in an attempt to lower the
number of possible erroneous parallax solutions entering our catalog.
However, the URAT reduction process does not take provisions for close
doubles (blended images) of arcsecond-level separations. Many of the
parallaxes, particularly those with large mean elongation, large
parallax error, large fit sigma and many rejected observations are
possibly blended images leading to a higher chance of an erroneous
parallax solutions. A visual inspection of all residual plots and real
sky images would not be practical for the entire catalog. However, we
have included information in the catalog to help the user to determine
if a solution should be investigated further.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
upc.dat 167 112177 URAT Parallax Catalog
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See also:
I/238 : Yale Trigonometric Parallaxes, Fourth Edition (van Altena+ 1995)
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
J/AJ/148/119 : UCAC4 nearby star survey (Finch+, 2014)
I/329 : URAT1 Catalog (Zacharias+ 2015)
Byte-by-byte Description of file: upc.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- UPC URAT Parallax Catalog (UPC) number
8- 18 F11.7 deg RAdeg Right ascension on ICRS, at Epoch J2014 (1)
20- 30 F11.7 deg DEdeg Declination on ICRS, at Epoch J2014 (1)
32- 61 A30 --- Name Identifier (2)
63- 67 F5.2 mag f.mag URAT mean model fit magnitude (3)
69- 74 F6.1 mas relpi URAT relative parallax
76- 78 F3.1 mas picor Parallax correction
80 A1 --- corflg [0-2] Parallax correction flag (4)
82- 87 F6.1 mas abspi Absolute parallax
89- 93 F5.1 mas e_abspi Error on absolute parallax
95-101 F7.1 mas/yr pmRA Proper motion in right ascension
103-107 F5.1 mas/yr e_pmRA Error proper motion in right ascension
109-115 F7.1 mas/yr pmDE Proper motion in Declination
117-121 F5.1 mas/yr e_pmDE Error proper motion in Declination
123-125 I3 --- ne Total number of epochs available (5)
127-128 I2 --- nr Total number of epochs rejected (5)
130-133 F4.2 yr Espan Epoch span of data
135-139 F5.3 --- Elo Average elongation of image (6)
141-145 F5.3 --- fsig1 Fit sigma 1 (reduced chi-square) (7)
147-151 F5.1 mas fsig2 Fit sigma 2 (mean error indiv.obs.)
153 A1 --- srcflg [0-5] Source flag (8)
155-161 F7.2 mas srcpi Parallax from external source (9)
163-167 F5.2 mas e_srcpi Parallax error from external source (9)
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Note (1): Positions are on the International Celestial Reference System
(ICRS) as represented by the UCAC4 catalog. Mean observed positions
are given at epoch J2014 (mean observed positions have been updated
to J2014 using the proper motions from column ('pmRA', 'pmDE').
Note (2): Identifier comes from the external source from which the URAT
position was matched column ('srcflg'). For Mearth the LSPM North
Catalog Designation is given. This is left blank if no identifier
was found.
Note (3): This is the mean, observed magnitude in the 680-750 nm URAT
bandpass, calibrated by APASS photometry. This bandpass is between
R and I, thus further into the red than UCAC. Observations in
non-photometric nights *are* included thus the URAT magnitudes need
to be taken with caution.
Note (4): The parallax correction flag is as follows:
0 = correction from the photometric parallaxes of UCAC4 ref.stars
1 = no correction so the mean of 1.3mas was used
2 = large correction so the cut off of 3.9mas was used
Note (5): the number of epochs available in the URAT epoch data (ne) and
the number of epochs rejected (nr) during the fit solutions.
Note (6): average image elongation from moment analysis, ratio of major
to minor axis is given (1.0 = round)
Note (7): The error of unit weight (reduced chi-square) of the parallax fit
solution is given. Thus 1.0 means the scatter of the post-fit residuals
match the expected observational errors and assigned weights.
Note (8): The source flag gives the external source to which the URAT
position was matched and where the information for columns 'srcpi'
and e_srcpi are from.
0 = no match to any of the following external catalogs found
1 = matched to Hipparcos (Cat. I/239)
2 = matched with The Yale Parallax Catalog
(van Altena et al., 1995, Cat. I/238)
3 = matched with (Finch & Zacharias, 2016, AJ, in press)
4 = matched with MEarth parallaxes
(Dittmann et. al., 2014ApJ...784..156D 2014ApJ...784..156D)
5 = matched with SIMBAD database (http://simbad.u-strasbg.fr/simbad/)
Note (9): Parallax and error from external source. Due to the
limitations of the SIMBAD database automated search feature the
parallax error or the source of the parallax is not given so for
all srcflg = 5, the parallax error is reported as 0.0. For all
srcflg = 0, meaning no match to an external catalog the parallax
and error are reported as 0.0.
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Acknowledgements:
Charlie Finch, charlie.finch(at)usno.navy.mil
(End) Patricia Vannier [CDS] 06-Apr-2016