2,413 research outputs found
Precise Ages of Field Stars from White Dwarf Companions
Observational tests of stellar and Galactic chemical evolution call for the
joint knowledge of a star's physical parameters, detailed element abundances,
and precise age. For cool main-sequence (MS) stars the abundances of many
elements can be measured from spectroscopy, but ages are very hard to
determine. The situation is different if the MS star has a white dwarf (WD)
companion and a known distance, as the age of such a binary system can then be
determined precisely from the photometric properties of the cooling WD. As a
pilot study for obtaining precise age determinations of field MS stars, we
identify nearly one hundred candidates for such wide binary systems: a faint WD
whose GPS1 proper motion matches that of a brighter MS star in Gaia/TGAS with a
good parallax (). We model the WD's multi-band
photometry with the BASE-9 code using this precise distance (assumed to be
common for the pair) and infer ages for each binary system. The resulting age
estimates are precise to () for () MS-WD systems.
Our analysis more than doubles the number of MS-WD systems with precise
distances known to date, and it boosts the number of such systems with precise
age determination by an order of magnitude. With the advent of the Gaia DR2
data, this approach will be applicable to a far larger sample, providing ages
for many MS stars (that can yield detailed abundances for over 20 elements),
especially in the age range 2 to 8\,\Gyr, where there are only few known star
clusters.Comment: 9 pages, 5 figures, 1 catalog; Submitted to Ap
The Right to Innovate
Article published in the Michigan State Law Review
Self-Regulation and Power: How Self-Regulatory Failures Can Enhance Social Power
© 2016 John Wiley & Sons Ltd. Low self-control is often associated with poor life outcomes. Here, we propose that self-control failures may also provide social benefits by signaling and maintaining power. We identify several pathways by which reduced self-control can assist in ascending social hierarchies. First, the self-enhancing tendencies adopted by people with low self-control may contribute to making positive first impressions and advertising power to new acquaintances. The direct and disinhibited communication styles that stem from self-control failures may also enhance power and lubricate difficult social interactions. Disinhibited aggression can help people maintain and acquire material resources and establish dominance over rivals. Finally, the parallels between the behavior of people with low self-control and people with power (e.g., self-enhancement, disinhibition, approach-orientation, aggression) suggest that people with impaired self-control will be perceived as more powerful than people with intact self-control. Evidence for these propositions and directions for future research are discussed
The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs
We present a detailed analysis of the white dwarf luminosity functions
derived from the local 40 pc sample and the deep proper motion catalog of Munn
et al (2014, 2017). Many of the previous studies ignored the contribution of
thick disk white dwarfs to the Galactic disk luminosity function, which results
in an erronous age measurement. We demonstrate that the ratio of thick/thin
disk white dwarfs is roughly 20\% in the local sample. Simultaneously fitting
for both disk components, we derive ages of 6.8-7.0 Gyr for the thin disk and
8.7 0.1 Gyr for the thick disk from the local 40 pc sample. Similarly, we
derive ages of 7.4-8.2 Gyr for the thin disk and 9.5-9.9 Gyr for the thick disk
from the deep proper motion catalog, which shows no evidence of a deviation
from a constant star formation rate in the past 2.5 Gyr. We constrain the time
difference between the onset of star formation in the thin disk and the thick
disk to be Gyr. The faint end of the luminosity function
for the halo white dwarfs is less constrained, resulting in an age estimate of
Gyr for the Galactic inner halo. This is the first time
ages for all three major components of the Galaxy are obtained from a sample of
field white dwarfs that is large enough to contain significant numbers of disk
and halo objects. The resultant ages agree reasonably well with the age
estimates for the oldest open and globular clusters.Comment: ApJ, in pres
Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters II: NGC 5024, NGC 5272, and NGC 6352
We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival
ACS Treasury observations of Galactic Globular Clusters to find and
characterize two stellar populations in NGC 5024 (M53), NGC 5272 (M3), and NGC
6352. For these three clusters, both single and double-population analyses are
used to determine a best fit isochrone(s). We employ a sophisticated Bayesian
analysis technique to simultaneously fit the cluster parameters (age, distance,
absorption, and metallicity) that characterize each cluster. For the
two-population analysis, unique population level helium values are also fit to
each distinct population of the cluster and the relative proportions of the
populations are determined. We find differences in helium ranging from
0.05 to 0.11 for these three clusters. Model grids with solar
-element abundances ([/Fe] =0.0) and enhanced -elements
([/Fe]=0.4) are adopted.Comment: ApJ, 21 pages, 14 figures, 7 table
WIYN Open Cluster Study 1: Deep Photometry of NGC 188
We have employed precise V and I photometry of NGC 188 at WIYN to explore the
cluster luminosity function (LF) and study the cluster white dwarfs (WDs). Our
photometry is offset by V = 0.052 (fainter) from Sandage (1962) and Eggen &
Sandage (1969). All published photometry for the past three decades have been
based on these two calibrations, which are in error by 0.05 +- 0.01. We employ
the Pinsonneault etal (1998) fiducial main sequence to derive a cluster
distance modulus of 11.43 +- 0.08. We report observations that are >= 50%
complete to V = 24.6 and find that the cluster central-field LF peaks at M_I ~
3 to 4. This is unlike the solar neighborhood LF and unlike the LFs of
dynamically unevolved portions of open and globular clusters, which rise
continuously until M_I ~ 9.5. Although we find that >= 50% of the unresolved
cluster objects are multiple systems, their presence cannot account for the
shape of the NGC 188 LF. For theoretical reasons (Terlevich 1987; Vesperini &
Heggie 1997) having to do with the survivability of NGC 188 we believe the
cluster is highly dynamically evolved and that the missing low luminosity stars
are either in the cluster outskirts or have left the cluster altogether. We
identify nine candidate WDs, of which we expect three to six are bona fide
cluster WDs. The luminosities of the faintest likely WD indicates an age
(Bergeron, Wesemael, & Beauchamp 1995) of 1.14 +- 0.09 Gyrs. This is a lower
limit to the cluster age and observations probing to V = 27 or 28 will be
necessary to find the faintest cluster WDs and independently determine the
cluster age. While our age limit is not surprising for this ~6 Gyr old cluster,
our result demonstrates the value of the WD age technique with its very low
internal errors. (abridged)Comment: 26 pages, uuencoded gunzip'ed latex + 16 postscrip figures, to be
published in A
Precise Ages of Field Stars from White Dwarf Companions
Observational tests of stellar and Galactic chemical evolution call for the joint knowledge of a star’s physical parameters, detailed element abundances, and precise age. For cool main-sequence (MS) stars the abundances of many elements can be measured from spectroscopy, but ages are very hard to determine. The situation is different if the MS star has a white dwarf (WD) companion and a known distance, as the age of such a binary system can then be determined precisely from the photometric properties of the cooling WD. As a pilot study for obtaining precise age determinations of field MS stars, we identify nearly one hundred candidate for such wide binary systems: a faint WD whose GPS1 proper motion matches that of a brighter MS star in Gaia/TGAS with a good parallax (σ ≤ 0.05). We model the WD’s multi-band photometry with the BASE-9 code using this precise distance (assumed to be common for the pair) and infer ages for each binary system. The resulting age estimates are precise to ≤ 10% (≤ 20%) for 42 (67) MS-WD systems. Our analysis more than doubles the number of MS-WD systems with precise distances known to date, and it boosts the number of such systems with precise age determination by an order of magnitude. With the advent of the Gaia DR2 data, this approach will be applicable to a far larger sample, providing ages for many MS stars (that can yield detailed abundances for over 20 elements), especially in the age range 2 to 8 Gyr, where there are only few known star clusters
New Techniques to Determine Ages of Open Clusters Using White Dwarfs
Currently there are two main techniques for independently determining the
ages of stellar populations: main sequence evolution theory (via cluster
isochrones) and white dwarf cooling theory. Open clusters provide the ideal
environment for the calibration of these two clocks. Because current techniques
to derive cluster ages from white dwarfs are observationally challenging, we
discuss the feasibility of determining white dwarf ages from the brighter white
dwarfs alone. This would eliminate the requirement of observing the coolest
(i.e., faintest) white dwarfs. We discuss our method for testing this new idea,
as well as the required photometric precision and prior constraints on
metallicity, distance, and reddening. We employ a new Bayesian statistical
technique to obtain and interpret results.Comment: 15 pages, 5 figures. accepted to Astrophysical Journa
Modeling transcription factor binding events to DNA using a random walker/jumper representation on a 1D/2D lattice with different affinity sites
Surviving in a diverse environment requires corresponding organism responses.
At the cellular level, such adjustment relies on the transcription factors
(TFs) which must rapidly find their target sequences amidst a vast amount of
non-relevant sequences on DNA molecules. Whether these transcription factors
locate their target sites through a 1D or 3D pathway is still a matter of
speculation. It has been suggested that the optimum search time is when the
protein equally shares its search time between 1D and 3D diffusions. In this
paper, we study the above problem using a Monte Carlo simulation by considering
a very simple physical model. A 1D strip, representing a DNA, with a number of
low affinity sites, corresponding to non-target sites, and high affinity sites,
corresponding to target sites, is considered and later extended to a 2D strip.
We study the 1D and 3D exploration pathways, and combinations of the two modes
by considering three different types of molecules: a walker that randomly walks
along the strip with no dissociation; a jumper that represents dissociation and
then re-association of a TF with the strip at later time at a distant site; and
a hopper that is similar to the jumper but it dissociates and then
re-associates at a faster rate than the jumper. We analyze the final
probability distribution of molecules for each case and find that TFs can
locate their targets fast enough even if they spend 15% of their search time
diffusing freely in the solution. This indeed agrees with recent experimental
results obtained by Elf et al. 2007 and is in contrast with theoretical
expectation.Comment: 24 pages, 9 figure
- …