97 research outputs found
Implications for the Formation of Blue Straggler Stars from HST Ultraviolet Observations of NGC 188
We present results of a Hubble Space Telescope far-ultraviolet (FUV) survey
searching for white dwarf (WD) companions to blue straggler stars (BSSs) in
open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined
binaries with properties suggestive of mass-transfer formation via Roche lobe
overflow, specifically through an asymptotic giant branch star transferring
mass to a main sequence secondary, yielding a BSS binary with a WD companion.
In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a
WD companion hot and luminous enough to be directly detected as a FUV
photometric excess with HST. Comparing expected BSS FUV emission to observed
photometry reveals four BSSs with WD companions above 12,000 K (younger than
250 Myr) and three WD companions with temperatures between 11,000-12,000 K.
These BSS+WD binaries all formed through recent mass transfer. The location of
the young BSSs in an optical color-magnitude diagram (CMD) indicates that
distance from the zero-age main sequence does not necessarily correlate with
BSS age. There is no clear CMD separation between mass transfer-formed BSSs and
those likely formed through other mechanisms, such as collisions. The seven
detected WD companions place a lower limit on the mass-transfer formation
frequency of 33%. We consider other possible formation mechanisms by comparing
properties of the BSS population to theoretical predictions. We conclude that
14 BSS binaries likely formed from mass transfer, resulting in an inferred
mass-transfer formation frequency of approximately 67%.Comment: 13 pages, 6 figures, accepted to the Astrophysical Journa
Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
Several possible formation pathways for blue straggler stars have been
developed recently, but no one pathway has yet been observationally confirmed
for a specific blue straggler. Here we report the first findings from a Hubble
Space Telescope ACS/SBC far-UV photometric program to search for white dwarf
companions to blue straggler stars. We find three hot and young white dwarf
companions to blue straggler stars in the 7-Gyr open cluster NGC 188,
indicating that mass transfer in these systems ended less than 300 Myr ago.
These companions are direct and secure observational evidence that these blue
straggler stars were formed through mass transfer in binary stars. Their
existence in a well-studied cluster environment allows for observational
constraints of both the current binary system and the progenitor binary system,
mapping the entire mass transfer history.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Journal of Experimental & Clinical Assisted Reproduction: shaping the future of research and practice in reproductive endocrinology/infertility
Journal of Experimental & Clinical Assisted Reproduction is an open access, online, peer-review journal publishing papers on all aspects of research into reproductive endocrinology, infertility, bioethics and the advanced reproductive technologies. The journal reports on important developments impacting the field of human reproductive medicine and surgery. The field exists as a sub-specialty of obstetrics & gynecology, focusing on the diagnosis and treatment of complex human reproductive problems. The continued growth of this relatively new field depends on quality research by proven scientists as well as junior investigators who, together, make contributions to this area of medical and surgical practice. The publishing revolution made possible by internet technology presages a bright future for continued interdisciplinary collaboration among researchers. Against this background, Journal of Experimental & Clinical Assisted Reproduction exists for the scientific community to facilitate this scholarly dialogue
The Color-Period Diagram and Stellar Rotational Evolution - New Rotation Period Measurements in the Open Cluster M34
We present results from a 5-month photometric survey for stellar rotation
periods combined with a 4-year radial-velocity survey for membership and
binarity in the 220Myr open cluster M34. We report surface rotation periods for
120 stars, 83 of which are late-type cluster members. A comparison to previous
work serves to illustrate the importance of high cadence long baseline
photometric observations and membership information. The new M34 periods are
less biased against slow rotation and cleaned for non-members. The rotation
periods of the cluster members span more than an order of magnitude from 0.5
day up to 11.5 days, and trace two distinct rotational sequences - fast (C) and
moderate-to-slow (I) - in the color-period diagram. The sequences represent two
different states in the rotational evolution of the late-type cluster members.
We use the color-period diagrams for M34 and for younger and older clusters to
estimate the timescale for the transition from the C to the I sequence and find
~<150Myr, ~150-300Myr, and ~300-600Myr for G, early-mid K, and late K dwarfs,
respectively. The small number of stars in the gap between C and I suggest a
quick transition. We estimate a lower limit on the maximum spin-down rate
(dP/dt) during this transition to be ~0.06 days/Myr and ~0.08 days/Myr for
early and late K dwarfs, respectively. We compare the I sequence rotation
periods in M34 and the Hyades for G and K dwarfs and find that K dwarfs spin
down slower than the Skumanich rate. We determine a gyrochronology age of
240Myr for M34. We measure the effect of cluster age uncertainties on the
gyrochronology age for M34 and find the resulting error to be consistent with
the error estimate for the technique. We use the M34 I sequence to redetermine
the coefficients in the expression for rotational dependence on color used in
gyrochronology (abridged).Comment: 47 pages (12pt, preprint), 14 figures, 2 tables, Accepted for
publication in ApJ, format of RA coordinates in Table 2 corrected in latest
versio
Electrophysiologic changes following treatment with organophosphorus-induced delayed neuropathy-producing agents in the adult hen
Although clinical, pathological, and biochemical effects of organophosphorus-induced delayed neuropathy (OPIDN) have been intensively investigated in the adult hen, detailed electrophysiological studies are lacking. Adult white leghorn hens were treated with a single oral dose of either 30 mg/kg tri-2-cresyl phosphate (TOCP), 750 mg/kg TOCP, 4 mg/kg di-n-butyl-2,2-dichlorovinyl phosphate (DBCV), or 30 mg/kg di-n-butyl-2,2-dichlorovinyl phosphinate (DBCV-P). The 750 mg/kg TOCP and DBCV, but not the 30 mg/kg TOCP and DBCV-P, treatments resulted in clinical signs of OPIDN and mild to marked damage of the tibial nerve 21 days after dose. Twenty-four hr lymphocyte neurotoxic esterase (NTE) inhibition was used as an index of brain NTE inhibition for the various organophosphorus compound (OP) treatment. Twenty-four hr lymphocyte NTE inhibition for 30 mg/kg TOCP, 750 mg/kg TOCP, DBCV, and DBCV-P was 54.1, 87.1, 84.8, and 68.3%, respectively. Twenty-one days after dose, the TOCP-treated hens exhibited some abnormalities in conduction velocity and action potential duration in the tibial or sciatic nerves. No abnormalities were observed in action potential parameters of either the DBCV or DBCV-P treatments. Neurotoxic OP (TOCP and DBCV) treatment resulted in decreased refractoriness in the tibial nerve, increased refractoriness in the sciatic nerve, and elevated strength duration threshold for both nerves. These changes were not present in nerves from DBCV-P (a non-neurotoxic NTE inhibitor)-treated hens. These results suggest that refractory period and strength duration abnormalities in peripheral nerve correlated well with the production of OPIDN and are evident without coincident clinical signs or histopathology.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26771/1/0000323.pd
Prospective associations of perceived unit cohesion with postdeployment mental health outcomes
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149506/1/da22884_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149506/2/da22884.pd
Stellar Rotation in M35: Mass-Period Relations, Spin-Down Rates, and Gyrochronology
We present the results of a 5 month photometric time-series survey for
stellar rotation over a 40'x40' field on the 150 Myr open cluster M35. We
report rotation periods for 441 stars and determine their cluster membership
and binarity based on a decade-long radial-velocity survey, proper-motion
measurements, and multi-band photometric observations. We find that 310 of the
stars with measured rotation periods are late-type members of M35. Their
distribution of rotation periods span more than two orders of magnitude from
~0.1-15 days, not constrained by the sampling frequency and the time-span of
the survey. With an age between the zero-age main-sequence and the Hyades, and
with ~6 times more rotation periods than measured in the Pleiades, M35 permit
detailed studies of early rotational evolution of late-type stars. Nearly 80%
of the 310 rotators lie on two distinct sequences in the color-period plane,
defining clear relations between stellar rotation period and color (mass). The
M35 color-period diagram enables us to determine timescales for the transition
between the two rotational states for G and K dwarfs, respectively. These
timescales are inversely related to the mass of the convective envelope, and
offer constraints on the rates of internal and external angular momentum
transport and of the evolution of stellar dynamos. A comparison to the Hyades,
confirm the Skumanich (1972) spindown-dependence for G dwarfs on one rotational
state, but suggest that K dwarfs spin down more slowly. The locations of the
rotational sequences in the M35 color-period diagram support the use of
rotational isochrones to determine ages for coeval stellar populations. We use
such gyrochronology to determine "gyro-ages" for M35. We use the M35 data to
evaluate new color dependencies for the rotational isochrones.Comment: 73 pages, 16 figures, Accepted for publication in ApJ. Replacement
reflect minor changes suggested by refere
The Effect of Pre-Main Sequence Stars on Star Cluster Dynamics
We investigate the effects of the addition of pre-main sequence evolution to
star cluster simulations. We allowed stars to follow pre-main sequence tracks
that begin at the deuterium burning birthline and end at the zero age main
sequence. We compared our simulations to ones in which the stars began their
lives at the zero age main sequence, and also investigated the effects of
particular choices for initial binary orbital parameters. We find that the
inclusion of the pre-main sequence phase results in a slightly higher core
concentration, lower binary fraction, and fewer hard binary systems. In
general, the global properties of star clusters remain almost unchanged, but
the properties of the binary star population in the cluster can be dramatically
modified by the correct treatment of the pre-main sequence stage.Comment: 40 pages ApJ preprint style Accepted by Ap
Consensus Statement on Concussion in Sportâ The 4th International Conference on Concussion in Sport Held in Zurich, November 2012
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147044/1/pmr2255.pd
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