89 research outputs found
The Solar Neighborhood XXV: Discovery of New Proper Motion Stars with 0.40 "/yr > mu > 0.18 "/yr between Declinations -47 degrees and 00 degrees
We present 2817 new southern proper motion systems with 0.40 "/yr > mu > 0.18
"/yr and declination between -47 degrees and 00 degrees. This is a continuation
of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We
use the same photometric relations as previous searches to provide distance
estimates based on the assumption that the objects are single main sequence
stars. We find 79 new red dwarf systems predicted to be within 25 pc, including
a few new components of previously known systems. Two systems - SCR 1731-2452
at 9.5 pc and SCR 1746-3214 at 9.9 pc - are anticipated to be within 10 pc. We
also find 23 new white dwarf candidates with distance estimates of 15-66 pc, as
well as 360 new red subdwarf candidates. With this search, we complete the SCR
sweep of the southern sky for stars with mu > 0.18 "/yr and R_59F < 16.5,
resulting in a total of 5042 objects in 4724 previously unreported proper
motion systems. Here we provide selected comprehensive lists from our SCR
proper motion search to date, including 152 red dwarf systems estimated to be
within 25 pc (nine within 10 pc), 46 white dwarfs (ten within 25 pc), and 598
subdwarf candidates. The results of this search suggest that there are more
nearby systems to be found at fainter magnitudes and lower proper motion limits
than those probed so far.Comment: 47 pages, 16 of text. 7 figure
White Dwarfs in the Solar Neighborhood
The study of white dwarfs (WDs) provides insight into understanding WD formation rates, evolution, and space density. Individually, nearby WDs are excellent candidates for astrometric planetary searches because the astrometric signature is greater than for an identical, more distant WD system. As a population, a complete volume-limited sample is necessary to provide unbiased statistics; however, their intrinsic faintness has allowed some to escape detection.
The aim of this dissertation is to identify nearby WDs, accurately characterize them, and target a subset of potentially interesting WDs for follow-up analyses. The most unambiguous method of identifying new WDs is by their proper motions. After evaluating all previous southern hemisphere proper motion catalogs and selecting viable candidates, we embarked on our own southern hemisphere proper motion survey, the SuperCOSMOS-RECONS (SCR) survey. A number of interesting objects were discovered during the survey, including the 24th nearest star system -- an M dwarf with a brown dwarf companion. After a series of spectroscopic observations, a total of 56 new WD systems was identified (18 from the SCR survey and 38 from other proper motion surveys).
CCD photometry was obtained for most of the 56 new systems in an effort to model the physical parameters and obtain distance estimates via spectral energy distribution fitting. An independent distance estimate was also obtained by deriving a color-MV relation for several colors based on WDs with known distances. Any object whose distance estimate was within 25 pc was targeted for a trigonometric parallax via our parallax program, CTIOPI.
Currently, there are 62 WD systems on CTIOPI. A subset of 53 systems has enough data for at least a preliminary parallax (24 are definitive). Of those 53 systems, nine are previously known WDs within 10 pc that we are monitoring for perturbations from unseen companions, and an additional 29 have distances within 25 pc. Previously, there were 109 known WDs with parallaxes placing them within 25 pc; therefore, our effort has already increased the nearby sample by 27%. In addition, at least two objects show hints of perturbations from unseen companions and need follow-up analyses
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
The Trigonometric Parallax of the Brown Dwarf Planetary System 2MASSW J1207334-393254
We have measured a trigonometric parallax to the young brown dwarf 2MASSW
J1207334-393254. The distance [54.0 (+3.2,-2.8) pc] and space motion confirm
membership in the TW Hydrae Association. The primary is a ~25 M_jup brown
dwarf. We discuss the "planetary mass" secondary, which is certainly below the
deuterium-burning limit but whose colors and absolute magnitudes pose
challenges to our current understanding of planetary-mass objects.Comment: Accepted to the Astrophysical Journal Letter
The Solar Neighborhood XLII. Parallax Results from the CTIOPI 0.9-m Program --- Identifying New Nearby Subdwarfs Using Tangential Velocities and Locations on the H-R Diagram
Parallaxes, proper motions, and optical photometry are presented for 51
systems made up 37 cool subdwarf and 14 additional high proper motion systems.
Thirty-seven systems have parallaxes reported for the first time, 15 of which
have proper motions of at least 1"/yr. The sample includes 22 newly identified
cool subdwarfs within 100 pc, of which three are within 25 pc, and an
additional five subdwarfs from 100-160 pc. Two systems --- LSR 1610-0040 AB and
LHS 440 AB --- are close binaries exhibiting clear astrometric perturbations
that will ultimately provide important masses for cool subdwarfs.
We use the accurate parallaxes and proper motions provided here, combined
with additional data from our program and others to determine that effectively
all nearby stars with tangential velocities greater than 200 km s are
subdwarfs. We compare a sample of 167 confirmed cool subdwarfs to nearby main
sequence dwarfs and Pleiades members on an observational Hertzsprung-Russell
diagram using vs.~ to map trends of age and metallicity. We
find that subdwarfs are clearly separated for spectral types K5--M5, indicating
that the low metallicities of subdwarfs set them apart in the H-R diagram for
= 3--6. We then apply the tangential velocity cutoff and the
subdwarf region of the H-R diagram to stars with parallaxes from {\it Gaia}
Data Release 1 and the MEarth Project to identify a total of 29 new nearby
subdwarf candidates that fall clearly below the main sequence.Comment: accepted for publication in Astronomical Journa
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
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