325 research outputs found
The effect of a literature intervention program on children\u27s attitudes toward the elderly
Nearby Red Dwarfs and Their Dance Partners: Characterizing More Than 2000 Single and Multiple M Dwarfs Near the Sun
This dissertation presents the results of a study to (1) determine the census of the nearby southern M dwarf stellar population via three types of distances and (2) determine the multiplicity rate of nearby M dwarfs using two different search methodologies.
The first part of this work reports three types of distance calculations (photographic, photometric, and trigonometric) for 1748 southern M dwarfs. Distances were estimated for 500 red dwarfs using photographic plate BRI magnitudes from SuperCOSMOS, while estimates were made for 667 stars using CCD VRI magnitudes. Both BRI and VRI were combined with 2MASS infrared JHK magnitudes. Distances for an additional 581 red dwarfs were derived from trigonometric parallaxes, 124 of which were measured for the first time during this work.
For the second portion of this thesis, an all-sky sample of 1122 M dwarfs, known via trigonometric parallaxes to lie within 25 pc of the Sun, was surveyed for stellar companions at separations of 2 to 600 . I-band images using primarily the CTIO/SMARTS 0.9m and the Lowell 42in telescopes were obtained in order to search these systems for companions at separations of 2 to 180 . A complementary reconnaissance of wider companions to 600 was also done via blinking SuperCOSMOS BRI images.
We find a stellar multiplicity fraction of 27.4 1.3% for M dwarfs. Using this new gauge of M dwarf multiplicity near the end of the stellar main sequence, we calculate a multiplicity fraction of 30.1% for stellar systems of all types, implying that most systems are single. We find a peak in the separation distribution of the companions at 26 AU, i.e., distances on the scale of our Solar System, with a weak trend of smaller projected separations for lower mass primaries. A hint that M dwarf multiplicity may be a function of age/composition was revealed, with faster moving (and generally older) systems being multiple slightly less often. We calculate that at least 16% of M dwarf mass is made up of the stellar companions of multiple systems. Finally, we show that the mass function for M dwarfs increases to the end of the main sequence
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
Distance Dependent Offsets between Parallaxes for Nearby Stars and Gaia DR1 Parallaxes
We use 612 single stars with previously published trigonometric parallaxes
placing them within 25 pc to evaluate parallaxes released in Gaia's first data
release (DR1). We find that the Gaia parallaxes are, on average, mas smaller than the weighted mean trigonometric parallax values for
these stars in the solar neighborhood. We also find that the offset changes
with distance out to 100 pc, in the sense that the closer the star, the larger
the offset. We find no systematic trends in the parallax offsets with stellar
magnitude, color, or proper motion. We do find that the offset is
roughly twice as large for stars south of the ecliptic compared to those that
are north.Comment: 14 pages, 2 figures, 3 tables, accepted for publication in ApJ
Letter. The table 1 is available in its entirety in a machine-readable form
in the online journa
The Solar Neighborhood. XXXIV. A Search for Planets Orbiting Nearby M Dwarfs using Astrometry
Astrometric measurements are presented for seven nearby stars with previously
detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ
1214) and one K dwarf (BD 10 3166). Measurements are also presented for six
additional nearby M dwarfs without known planets, but which are more favorable
to astrometric detections of low mass companions, as well as three binary
systems for which we provide astrometric orbit solutions. Observations have
baselines of three to thirteen years, and were made as part of the RECONS
long-term astrometry and photometry program at the CTIO/SMARTS 0.9m telescope.
We provide trigonometric parallaxes and proper motions for all 16 systems, and
perform an extensive analysis of the astrometric residuals to determine the
minimum detectable companion mass for the 12 M dwarfs not having close stellar
secondaries. For the six M dwarfs with known planets, we are not sensitive to
planets, but can rule out the presence of all but the least massive brown
dwarfs at periods of 2 - 12 years. For the six more astrometrically favorable M
dwarfs, we conclude that none have brown dwarf companions, and are sensitive to
companions with masses as low as 1 for periods longer than two years.
In particular, we conclude that Proxima Centauri has no Jovian companions at
orbital periods of 2 - 12 years. These results complement previously published
M dwarf planet occurrence rates by providing astrometrically determined upper
mass limits on potential super-Jupiter companions at orbits of two years and
longer. As part of a continuing survey, these results are consistent with the
paucity of super-Jupiter and brown dwarf companions we find among the over 250
red dwarfs within 25 pc observed longer than five years in our astrometric
program.Comment: 18 pages, 5 figures, 4 tables, accepted for publication in A
- …