82 research outputs found
The infrared counterpart of the Z source GX5-1
We have obtained UKIRT infrared observations of the field of the bright
Galactic Z source GX5-1. From an astrometric plate solution tied to Tycho-ACT
standards we have obtained accurate positions for the stars in our field which,
combined with an accurate radio position, have allowed us to identify the
probable infrared counterpart of GX5-1. Narrow-band photometry marginally
suggests excess Br-gamma emission in the counterpart, supporting its
association with an accretion-disc source. No significant variability is
observed in a limited number of observations. We compare the H and K magnitudes
with those of other Z sources, and briefly discuss possible sources of infrared
emission in these systems.Comment: 5 pages, 2 figures, accepted by MNRA
Faint Standards for ZYJHK from the UKIDSS and VISTA Surveys
The currently defined "UKIRT Faint Standards" have JHK magnitudes between 10
and 15, with K_median=11.2. These stars will be too bright for the next
generation of large telescopes. We have used multi-epoch observations taken as
part of the UKIRT Infrared Deep Sky Survey (UKIDSS) and the Visible and
Infrared Survey Telescope for Astronomy (VISTA) surveys to identify
non-variable stars with JHK magnitudes in the range 16-19. The stars were
selected from the UKIDSS Deep Extragalactic Survey (DXS) and Ultra Deep Survey
(UDS), the WFCAM calibration data (WFCAMCAL08B), the VISTA Deep Extragalactic
Observations (VIDEO) and UltraVISTA. Sources selected from the near-infrared
databases were paired with the Pan-STARRS Data Release 2 of optical to
near-infrared photometry and the Gaia astrometric Data Release 2. Colour
indices and other measurements were used to exclude sources that did not appear
to be simple single stars. From an initial selection of 169 sources, we present
a final sample of 81 standard stars with ZYJHK magnitudes, or a subset, each
with 20 to 600 observations in each filter. The new standards have
Ks_median=17.5. The relative photometric uncertainty for the sample is <0.006
mag and the absolute uncertainty is estimated to be <~0.02 mag. The sources are
distributed equatorially and are accessible from both hemispheres.Comment: Accepted on January 27 2020 for publication in MNRA
Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems
We present results of a reconnaissance for stellar companions to all 131
radial-velocity-detected candidate extrasolar planetary systems known as of
July 1, 2005. CPM companions were investigated using the multi-epoch DSS
images, and confirmed by matching the trigonometric parallax distances of the
primaries to companion distances estimated photometrically. We also attempt to
confirm or refute companions listed in the Washington Double Star Catalog, the
Catalogs of Nearby Stars, in Hipparcos results, and in Duquennoy & Mayor
(1991).
Our findings indicate that a lower limit of 30 (23%) of the 131 exoplanet
systems have stellar companions. We report new stellar companions to HD 38529
and HD 188015, and a new candidate companion to HD 169830. We confirm many
previously reported stellar companions, including six stars in five systems
that are recognized for the first time as companions to exoplanet hosts. We
have found evidence that 20 entries in the Washington Double Star Catalog are
not gravitationally bound companions. At least three, and possibly five, of the
exoplanet systems reside in triple star systems. Three exoplanet systems have
potentially close-in stellar companions ~ 20 AU away from the primary. Finally,
two of the exoplanet systems contain white dwarf companions. This comprehensive
assessment of exoplanet systems indicates that solar systems are found in a
variety of stellar multiplicity environments - singles, binaries, and triples;
and that planets survive the post-main-sequence evolution of companion stars.Comment: 52 pages, 7 figures, Accepted for publication in Ap
The Solar Neighborhood. XIX. Discovery and Characterization of 33 New Nearby White Dwarf Systems
We present spectra for 33 previously unclassified white dwarf systems
brighter than V = 17 primarily in the southern hemisphere. Of these new
systems, 26 are DA, 4 are DC, 2 are DZ, and 1 is DQ. We suspect three of these
systems are unresolved double degenerates. We obtained VRI photometry for these
33 objects as well as for 23 known white dwarf systems without trigonometric
parallaxes, also primarily in the southern hemisphere. For the 56 objects, we
converted the photometry values to fluxes and fit them to a spectral energy
distribution using the spectroscopy to determine which model to use (i.e. pure
hydrogen, pure helium, or metal-rich helium), resulting in estimates of
effective temperature and distance. Eight of the new and 12 known systems are
estimated to be within the NStars and Catalogue of Nearby Stars (CNS) horizons
of 25 pc, constituting a potential 18% increase in the nearby white dwarf
sample. Trigonometric parallax determinations are underway via CTIOPI for these
20 systems.
One of the DCs is cool so that it displays absorption in the near infrared.
Using the distance determined via trigonometric parallax, we are able to
constrain the model-dependent physical parameters and find that this object is
most likely a mixed H/He atmosphere white dwarf similar to other cool white
dwarfs identified in recent years with significant absorption in the infrared
due to collision-induced absorptions by molecular hydrogen.Comment: 33 pages, 10 figures, accepted for publication in the Astronomical
Journa
The Solar Neighborhood XXVII: Discovery of New Proper Motion Stars with mu > 0.18 "/yr in the Southern Sky with 16.5 > R_59F > 18.0
Here we present 1584 new southern proper motion systems with mu > 0.18 "/yr
and 16.5 > R_59F > 18.0. This search complements the six previous
SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky for stars
within the same proper motion range, but with R_59F < 16.5. As in previous
papers, we present distance estimates for these systems and find that three
systems are estimated to be within 25 pc, including one, SCR 1546-5534,
possibly within the RECONS 10 pc horizon at 6.7 pc, making it the second
nearest discovery of the searches. We find 97 white dwarf candidates with
distance estimates between 10 and 120 pc, as well as 557 cool subdwarf
candidates. The subdwarfs found in this paper make up nearly half of the
subdwarf systems reported from our SCR searches, and are significantly redder
than those discovered thus far. The SCR searches have now found 155 red dwarfs
estimated to be within 25 pc, including 10 within 10 pc. In addition, 143 white
dwarf candidates and 1155 cool subdwarf candidates have been discovered. The
1584 systems reported here augment the sample of 4724 systems previously
discovered in our SCR searches, and imply that additional systems fainter than
R_59F = 18.0 are yet to be discovered.Comment: 11 pages of text, seven figure
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