157 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
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 VIII: Discovery of New High Proper Motion Nearby Stars Using the SuperCOSMOS Sky Survey
Five new objects with proper motions between 1.0 arcsec/yr and 2.6 arcsec/yr
have been discovered via a new RECONS search for high proper motion stars
utilizing the SuperCOSMOS Sky Survey. The first portion of the search,
discussed here, is centered on the south celestial pole and covers declinations
-90 degrees to -57.5 degrees.
Photographic photometry from SuperCOSMOS and JHKs near-infrared photometry
from 2MASS for stars nearer than 10 pc are combined to provide a suite of new
M_Ks-color relations useful for estimating distances to main sequence stars.
These relations are then used to derive distances to the new proper motion
objects as well as previously known stars with mu >= 1.0 arcsec/yr (many of
which have no trigonometric parallaxes) recovered during this phase of the
survey.
Four of the five new stars have red dwarf colors, while one is a nearby white
dwarf. Two of the red dwarfs are likely to be within the RECONS 10 pc sample,
and the white dwarf probably lies between 15 and 25 pc. Among the 23 known
stars recovered during the search, there are three additional candidates for
the RECONS sample that have no trigonometric parallaxes.Comment: 17 pages, 5 figures; accepted for publication in Astronomy Journa
UCAC3 Proper Motion Survey. I. Discovery of New Proper Motion Stars in UCAC3 with 0.40 "/yr > mu >= 0.18 "/yr between Declinations -90 deg and -47 deg
Presented here are 442 new proper motion stellar systems in the southern sky
between declinations -90\degr and -47\degr with 0\farcs40 yr
0\farcs18 yr. These systems constitute a 25.3% increase in
new systems for the same region of the sky covered by previous SuperCOSMOS
RECONS (SCR) searches that used Schmidt plates as the primary source of
discovery. Among the new systems are 25 multiples, plus an additional seven new
common proper motion companions found to previously known primaries. All stars
have been discovered using the third U.S. Naval Observatory (USNO) CCD
Astrograph Catalog (UCAC3). A comparison of the UCAC3 proper motions to those
from the Hipparcos, Tycho-2, Southern Proper Motion (SPM4), and SuperCOSMOS
efforts is presented, and shows that UCAC3 provides similar values and
precision to the first three surveys. The comparison between UCAC3 and
SuperCOSMOS indicates that proper motions in RA are systematically shifted in
the SuperCOSMOS data but are consistent in DEC data, while overall showing a
significantly higher scatter. Distance estimates are derived for stars having
SuperCOSMOS Sky Survey (SSS) , , and plate magnitudes
and Two-Micron All Sky Survey (2MASS) infrared photometry. We find 15 systems
estimated to be within 25 pc, including UPM 1710-5300 our closest new discovery
estimated at 13.5 pc. Such new discoveries suggest that more nearby stars are
yet to be found in these slower proper motion regimes, indicating that more
work is needed to develop a complete map of the solar neighborhood.Comment: 24 pages, 7 figures, 4 tables, accepted to the Astronomical Journal
July 07, 201
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
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
The Solar Neighborhood XXIII CCD Photometric Distance Estimates of SCR Targets -- 77 M Dwarf Systems within 25 Parsecs
We present CCD photometric distance estimates of 100 SCR (SuperCOSMOS RECONS)
systems with 0\farcs18/yr, 28 of which are new discoveries
previously unpublished in this series of papers. These distances are estimated
using a combination of new photometry acquired at CTIO and
magnitudes extracted from 2MASS. The estimates are improvements over those
determined using photographic plate magnitudes from SuperCOSMOS plus
, as presented in the original discovery papers. In total, 77 of the 100
systems investigated are predicted to be within 25 pc. If all 77 systems are
confirmed to have 40 milliarcseconds, this sample would
represent a 23% increase in M dwarf systems nearer than 25 pc in the southern
sky.Comment: 34 pages, 8 figure
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