J/MNRAS/480/4302 SDSS distant sample of halo wide binaries (Coronado+, 2018)
A distant sample of halo wide binaries from SDSS.
Coronado J., Sepulveda M.P., Gould A., Chaname J.
<Mon. Not. R. Astron. Soc., 480, 4302-4313 (2018)>
=2018MNRAS.480.4302C 2018MNRAS.480.4302C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Positional data ; Radial velocities;
Proper motions ; Optical
Keywords: catalogues - astrometry - binaries: general -
stars: kinematics and dynamics
Abstract:
Samples of reliably identified halo wide binaries are scarce. If
reasonably free from selection effects and with a small degree of
contamination by chance alignments, these wide binaries become a
powerful dynamical tool, having provided one of the very few
experiments capable of constraining the nature of dark matter in the
Milky Way halo. Currently, however, the best available sample of halo
wide binaries is confined to the solar neighbourhood, and is plagued
by small number statistics at the widest separations. We present the
results of a programme aimed to probe the wide binary population of
the Galactic halo at significantly larger distances, and which informs
future searches that could improve the statistics by orders of
magnitude. Halo stars were taken from the Sloan Digital Sky Survey
after analysing the Galactic orbits of stars in the reduced proper
motion diagram. We then select candidate binaries by searching for
pairs with small differences in proper motion and small projected
separation on the sky. Using medium-resolution spectroscopy, a
subsample of candidates is validated via radial velocities, finding
that about 68 per cent of candidate pairs up to 20arcsec separation
can be considered genuine halo wide binaries, to the limits of the
available data. Precise parallaxes from Gaia confirm that most of our
selected pairs have their components at the same distances,
independently confirming the robustness of our selection method. These
results should prove valuable to guide the optimal assembly of larger
catalogues of halo wide binaries from upcoming large databases, e.g.
Gaia and LSST.
Description:
We selected our sample using proper motions and photometry from the
SDSS. We use DR9, which has the advantage of correcting errors in
proper motions, previously present for DR7 stars at low Galactic
latitudes. Using the aforementioned query, we choose stars from DR9
with SDSS r-band magnitudes 14<r<20 and proper motions
µ>30mas/yr. This latter imposed criterion over the proper
motions significantly decreases the density of stars, especially more
distant ones, which in turn considerably decreases the probability of
chance alignments. For the query, PSF magnitudes were chosen, with
their corresponding extinction coefficients. In order to have reliable
photometry we follow Sesar, Ivezic & Juric (2008ApJ...689.1244S 2008ApJ...689.1244S) to
select real sources.
For the candidates that passed our selection criteria, we obtained
long-slit spectra. Observations were carried with the COSMOS
instrument at the Blanco telescope in Cerro Tololo Inter-American
Observatory (CTIO) with the blue VPH grism covering a wavelength range
of 5600-9600Å and a 0.9arcsec slit reaching a spectral resolution
of ∼2100. Also with the EFOSC2 spectrograph at the New Technology
Telescope (NTT) in La Silla with grism #20 covering a wavelength range
of 6047-7147Å and a 0.5arcsec slit reaching a spectral resolution
of ∼3200. Finally, with the KOSMOS instrument at the Kitt Peak
National Observatory (KPNO) with the red VPH grism covering a
wavelength range of 5600-9600Å and a 0.9 arcsec slit reaching a
spectral resolution of ∼2200. From the initial sample of 400 candidate
pairs, we obtained spectra for 88 pairs.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablec1.dat 162 88 Catalog of halo wide binaries
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- ID Identifier for each star
4- 15 F12.8 deg RAdeg Right ascension of star 1 (J2000)
17- 28 F12.8 deg DEdeg Declination of star 1 (J2000)
30- 41 F12.8 deg RA2deg Right ascension of star 2 (J2000)
43- 54 F12.8 deg DE2deg Declination of star 2 (J2000)
56- 67 F12.7 mas/yr pmGLON1 Proper motion in galactic longitude star 1
69- 79 F11.6 mas/yr pmGLON2 Proper motion in galactic longitude star 2
81- 91 F11.6 mas/yr pmGLAT1 Proper motion in galactic latitude star 1
93-105 F13.8 mas/yr pmGLAT2 Proper motion in galactic latitude star 2
107-115 F9.6 mag rmag1 PSF magnitude in the r band star 1
117-125 F9.6 mag rmag2 PSF magnitude in the r band star 2
127-136 F10.6 arcsec Sep Angular separation of the pair
138-144 F7.2 km/s RV1 Radial velocity of star 1
146-149 F4.1 km/s e_RV1 Error on RV1
151-157 F7.2 km/s RV2 Radial velocity of star 2
159-162 F4.1 km/s e_RV2 Error on RV2
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 27-May-2022