2,161 research outputs found
The Stellar Populations of Praesepe and Coma Berenices
We present the results of a stellar membership survey of the nearby open
clusters Praesepe and Coma Berenices. We have combined archival survey data
from the SDSS, 2MASS, USNOB1.0, and UCAC-2.0 surveys to compile proper motions
and photometry for ~5 million sources over 300 deg^2. Of these sources, 1010
stars in Praesepe and 98 stars in Coma Ber are identified as candidate members
with probability >80%; 442 and 61 are identified as high-probability candidates
for the first time. We estimate that this survey is >90% complete across a wide
range of spectral types (F0 to M5 in Praesepe, F5 to M6 in Coma Ber). We have
also investigated the stellar mass dependence of each cluster's mass and radius
in order to quantify the role of mass segregation and tidal stripping in
shaping the present-day mass function and spatial distribution of stars.
Praesepe shows clear evidence of mass segregation across the full stellar mass
range; Coma Ber does not show any clear trend, but low number statistics would
mask a trend of the same magnitude as in Praesepe. The mass function for
Praesepe (t~600 Myr; M~500 Msun) follows a power law consistent with that of
the field present-day mass function, suggesting that any mass-dependent tidal
stripping could have removed only the lowest-mass members (<0.15 Msun). Coma
Ber, which is younger but much less massive (t~400 Myr; M~100 Msun), follows a
significantly shallower power law. This suggests that some tidal stripping has
occurred, but the low-mass stellar population has not been strongly depleted
down to the survey completeness limit (~0.12 Msun).Comment: Accepted to AJ; 14 pages, 10 figures, 5 tables + 2 online-only table
Hot Stars With Cool Companions
Young intermediate-mass stars have become high-priority targets for
direct-imaging planet searches following the recent discoveries of planets
orbiting e.g. HR 8799 and Beta Pictoris. Close stellar companions to these
stars can affect the formation and orbital evolution of any planets, and so a
census of the multiplicity properties of nearby intermediate mass stars is
needed. Additionally, the multiplicity can help constrain the important binary
star formation physics. We report initial results from a spectroscopic survey
of 400 nearby A- and B-type stars. We search for companions by
cross-correlating high resolution and high signal-to-noise ratio echelle
spectra of the targets stars against model spectra for F- to M-type stars. We
have so far found 18 new candidate companions, and have detected the spectral
lines of the secondary in 4 known spectroscopic binary systems. We present the
distribution of mass-ratios for close companions, and find that it differs from
the distribution for wide ( AU) intermediate-mass binaries, which may
indicate a different formation mechanism for the two populations.Comment: Submitted as part of the 18th Cambridge Workshop on Cool Stars,
Stellar Systems, and the Sun Proceedings of Lowell Observatory (9-13 June
2014
Correcting For Telluric Absorption: Methods, Case Studies, And Release Of The TelFit Code
Ground-based astronomical spectra are contaminated by the Earth's atmosphere to varying degrees in all spectral regions. We present a Python code that can accurately fit a model to the telluric absorption spectrum present in astronomical data, with residuals of similar to 3%-5% of the continuum for moderately strong lines. We demonstrate the quality of the correction by fitting the telluric spectrum in a nearly featureless A0V star, HIP 20264, as well as to a series of dwarf M star spectra near the 819 nm sodium doublet. We directly compare the results to an empirical telluric correction of HIP 20264 and find that our model-fitting procedure is at least as good and sometimes more accurate. The telluric correction code, which we make freely available to the astronomical community, can be used as a replacement for telluric standard star observations for many purposes.UT Austin Hutchinson fellowshipUniversity of TexasAstronom
Testing the Metal of Late-Type Kepler Planet Hosts with Iron-Clad Methods
It has been shown that F, G, and early K dwarf hosts of Neptune-sized planets
are not preferentially metal-rich. However, it is less clear whether the same
holds for late K and M dwarf planet hosts. We report metallicities of Kepler
targets and candidate transiting planet hosts with effective temperatures below
4500 K. We use new metallicity calibrations to determine [Fe/H] from visible
and near-infrared spectra. We find that the metallicity distribution of late K
and M dwarfs monitored by Kepler is consistent with that of the solar
neighborhood. Further, we show that hosts of Earth- to Neptune-sized planets
have metallicities consistent with those lacking detected planets and rule out
a previously claimed 0.2 dex offset between the two distributions at 6sigma
confidence. We also demonstrate that the metallicities of late K and M dwarfs
hosting multiple detected planets are consistent with those lacking detected
planets. Our results indicate that multiple terrestrial and Neptune-sized
planets can form around late K and M dwarfs with metallicities as low as 0.25
of the solar value. The presence of Neptune-sized planets orbiting such
low-metallicity M dwarfs suggests that accreting planets collect most or all of
the solids from the disk and that the potential cores of giant planets can
readily form around M dwarfs. The paucity of giant planets around M dwarfs
compared to solar-type stars must be due to relatively rapid disk evaporation
or a slower rate of core accretion, rather than insufficient solids to form a
core.Comment: 9 pages, 5 figures. Accepted to Ap
The ability to move to a beat is linked to the consistency of neural responses to sound
The ability to synchronize movement to a steady beat is a fundamental skill underlying musical performance and has been studied for decades as a model of sensorimotor synchronization. Nevertheless, little is known about the neural correlates of individual differences in the ability to synchronize to a beat. In particular, links between auditory-motor synchronization ability and characteristics of the brain's response to sound have not yet been explored. Given direct connections between the inferior colliculus (IC) and subcortical motor structures, we hypothesized that consistency of the neural response to sound within the IC is linked to the ability to tap consistently to a beat. Here, we show that adolescent humans who demonstrate less variability when tapping to a beat have auditory brainstem responses that are less variable as well. One of the sources of this enhanced consistency in subjects who can steadily tap to a beat may be decreased variability in the timing of the response, as these subjects also show greater between-trial phase-locking in the auditory brainstem response. Thus, musical training with a heavy emphasis on synchronization of movement to musical beats may improve auditory neural synchrony, potentially benefiting children with auditory-based language impairments characterized by excessively variable neural responses
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