104 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
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. 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
Dwarf carbon stars are likely metal-poor binaries and unlikely hosts to carbon planets
Dwarf carbon stars make up the largest fraction of carbon stars in the Galaxy
with around 1200 candidates known to date primarily from the Sloan Digital Sky
Survey. They either possess primordial carbon-enhancements, or are polluted by
mass transfer from an evolved companion such that C/O is enhanced beyond unity.
To directly test the binary hypothesis, a radial velocity monitoring survey has
been carried out on 28 dwarf carbon stars, resulting in the detection of
variations in 21 targets. Using Monte Carlo simulations, this detection
fraction is found to be consistent with a 100% binary population and orbital
periods on the order of hundreds of days. This result supports the post-mass
transfer nature of dwarf carbon stars, and implies they are not likely hosts to
carbon planets.Comment: 5 pages, 1 figure, accepted to MNRA
The White Dwarfs within 20 Parsecs of the Sun: Kinematics and Statistics
We present the kinematical properties, distribution of spectroscopic
subtypes, stellar population subcomponents of the white dwarfs within 20 pc of
the sun. We find no convincing evidence of halo white dwarfs in the total 20 pc
sample of 129 white dwarfs nor is there convincing evidence of genuine thick
disk subcomponent members within 20 parsecs. Virtually the entire 20 pc sample
likely belongs to the thin disk. The total DA to non-DA ratio of the 20 pc
sample is 1.6, a manifestation of deepening envelope convection which
transforms DA stars with sufficiently thin H surface layers into non-DAs. The
addition of 5 new stars to the 20 pc sample yields a revised local space
density of white dwarfs of M_{\sun}/yr and a
corresponding mass density of M_{\sun}/pc.
We find that at least 15% of the white dwarfs within 20 parsecs of the sun (the
DAZ and DZ stars) have photospheric metals that possibly originate from
accretion of circumstellar material (debris disks) around them. If this
interpretation is correct, this suggests the possibility that the same
percentage have planets or asteroid-like bodies orbiting them.Comment: Accepted for publication in The 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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