1,345 research outputs found
SDSS J163030.58+423305.8: A 40 minute Orbital Period Detached White Dwarf Binary
We report the discovery of a new detached, double white dwarf system with an
orbital period of 39.8 min. We targeted SDSS J163030.58+423305.8 (hereafter
J1630) as part of our radial velocity program to search for companions around
low-mass white dwarfs using the 6.5m MMT. We detect peak-to-peak radial
velocity variations of 576 km/s. The mass function and optical photometry rule
out main-sequence companions. In addition, no milli-second pulsar companions
are detected in radio observations. Thus the invisible companion is most likely
another white dwarf. Unlike the other 39 min binary SDSS J010657.39-100003.3,
follow-up high speed photometric observations of J1630 obtained at the McDonald
2.1m telescope do not show significant ellipsoidal variations, indicating a
higher primary mass and smaller radius. The absence of eclipses constrain the
inclination angle to <82deg. J1630 contains a pair of white dwarfs, 0.3 Msun
primary + >0.3 Msun invisible secondary, at a separation of >0.32 Rsun. The two
white dwarfs will merge in less than 31 Myr. Depending on the core composition
of the companion, the merger will form either a single core-He burning subdwarf
star or a rapidly rotating massive white dwarf. The gravitational wave strain
from J1630 is detectable by instruments like the Laser Interferometer Space
Antenna (LISA) within the first year of operation.Comment: MNRAS Letters, in pres
A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey
We present optical spectroscopy and near-infrared photometry of 126 cool
white dwarfs in the Sloan Digital Sky Survey (SDSS). Our sample includes high
proper motion targets selected using the SDSS and USNO-B astrometry and a dozen
previously known ultracool white dwarf candidates. Our optical spectroscopic
observations demonstrate that a clean selection of large samples of cool white
dwarfs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic
Survey Telescope datasets) is possible using a reduced proper motion diagram
and a tangential velocity cut-off (depending on the proper motion accuracy) of
30 km/s. Our near-infrared observations reveal eight new stars with significant
absorption. We use the optical and near-infrared photometry to perform a
detailed model atmosphere analysis. More than 80% of the stars in our sample
are consistent with either pure hydrogen or pure helium atmospheres. However,
the eight stars with significant infrared absorption and the majority of the
previously known ultracool white dwarf candidates are best explained with mixed
hydrogen and helium atmosphere models. The age distribution of our sample is
consistent with a Galactic disk age of 8 Gyr. A few ultracool white dwarfs may
be as old as 12-13 Gyr, but our models have problems matching the spectral
energy distributions of these objects. There are only two halo white dwarf
candidates in our sample. However, trigonometric parallax observations are
required for accurate mass and age determinations and to confirm their
membership in the halo.Comment: ApJ Supplements, in pres
Protein phosphatase 1-dependent bidirectional synaptic plasticity controls ischemic recovery in the adult brain
Protein kinases and phosphatases can alter the impact of excitotoxicity resulting from ischemia by concurrently modulating apoptotic/survival pathways. Here, we show that protein phosphatase 1 (PP1), known to constrain neuronal signaling and synaptic strength (Mansuy et al., 1998; Morishita et al., 2001), critically regulates neuroprotective pathways in the adult brain. When PP1 is inhibited pharmacologically or genetically, recovery from oxygen/glucose deprivation (OGD) in vitro, or ischemia in vivo is impaired. Furthermore, in vitro, inducing LTP shortly before OGD similarly impairs recovery, an effect that correlates with strong PP1 inhibition. Conversely, inducing LTD before OGD elicits full recovery by preserving PP1 activity, an effect that is abolished by PP1 inhibition. The mechanisms of action of PP1 appear to be coupled with several components of apoptotic pathways, in particular ERK1/2 (extracellular signal-regulated kinase 1/2) whose activation is increased by PP1 inhibition both in vitro and in vivo. Together, these results reveal that the mechanisms of recovery in the adult brain critically involve PP1, and highlight a novel physiological function for long-term potentiation and long-term depression in the control of brain damage and repair
First Results from Pan-STARRS1: Faint, High Proper Motion White Dwarfs in the Medium-Deep Fields
The Pan-STARRS1 survey has obtained multi-epoch imaging in five bands
(Pan-STARRS1 gps, rps, ips, zps, and yps) on twelve "Medium Deep Fields", each
of which spans a 3.3 degree circle. For the period between Apr 2009 and Apr
2011 these fields were observed 50-200 times. Using a reduced proper motion
diagram, we have extracted a list of 47 white dwarf (WD) candidates whose
Pan-STARRS1 astrometry indicates a non-zero proper motion at the 6-sigma level,
with a typical 1-sigma proper motion uncertainty of 10 mas/yr. We also used
astrometry from SDSS (when available) and USNO-B to assess our proper motion
fits. None of the WD candidates exhibits evidence of statistically significant
parallaxes, with a typical 1-sigma uncertainty of 8 mas. Twelve of these
candidates are known WDs, including the high proper motion (1.7"/yr) WD LHS
291. We confirm three more objects as WDs through optical spectroscopy. Based
on the Pan-STARRS1 colors, ten of the stars are likely to be cool WDs with 4170
K Teff 5000 K and cooling ages <9 Gyr. We classify these objects as likely
thick disk WDs based on their kinematics. Our current sample represents only a
small fraction of the Pan-STARRS1 data. With continued coverage from the Medium
Deep Field Survey and the 3pi survey, Pan-STARRS1 should find many more high
proper motion WDs that are part of the old thick disk and halo.Comment: 33 pages, 8 figures, submitted to Ap
The Shortest Period Detached Binary White Dwarf System
We identify SDSS J010657.39-100003.3 (hereafter J0106-1000) as the shortest
period detached binary white dwarf (WD) system currently known. We targeted
J0106-1000 as part of our radial velocity program to search for companions
around known extremely low-mass (ELM, ~ 0.2 Msol) WDs using the 6.5m MMT. We
detect peak-to-peak radial velocity variations of 740 km/s with an orbital
period of 39.1 min. The mass function and optical photometry rule out a
main-sequence star companion. Follow-up high-speed photometric observations
obtained at the McDonald 2.1m telescope reveal ellipsoidal variations from the
distorted primary but no eclipses. This is the first example of a tidally
distorted WD. Modeling the lightcurve, we constrain the inclination angle of
the system to be 67 +- 13 deg. J0106-1000 contains a pair of WDs (0.17 Msol
primary + 0.43 Msol invisible secondary) at a separation of 0.32 Rsol. The two
WDs will merge in 37 Myr and most likely form a core He-burning single subdwarf
star. J0106-1000 is the shortest timescale merger system currently known. The
gravitational wave strain from J0106-1000 is at the detection limit of the
Laser Interferometer Space Antenna (LISA). However, accurate ephemeris and
orbital period measurements may enable LISA to detect J0106-1000 above the
Galactic background noise.Comment: MNRAS Letters, in pres
Expression des "activated leukocyte cell adhesion molecule" im Mammakarzinom: Prädiktivität für das Ansprechen auf eine taxanfreie Chemotherapie
Zusammenfassung: Ziele: "Activated leukocyte cell adhesion molecule" (ALCAM) ist ein Oberflächenimmunglobulin und wird in vielen Mammakarzinomen exprimiert. Es wird vermutet, dass ALCAM in der Tumorgenese und -progression eine Rolle spielt. Die Bedeutung des Adhäsionsmoleküls ALCAM für das Ansprechen auf eine taxanfreie adjuvante Chemotherapie wurde untersucht. Material und Methoden: Gewebeproben von 162Patientinnen mit Mammakarzinomen wurden im Hinblick auf die Expression des ALCAM-Proteins untersucht. Immunhistologische Untersuchungen (IHC) und Western-Blot-Analysen (WB) wurden mit einem monoklonalen Antikörper gegen ALCAM durchgeführt. Die Proteinmengen im WB wurden densitometrisch quantifiziert und mit klinischen sowie histologischen Parametern korreliert. Die Ergebnisse wurden auf mRNA-Ebene mithilfe der Microarray-Analysen (Affymetrix) validiert. Ergebnisse: In der normalen Brustdrüse wird ALCAM in den luminalen und den basalen Epithelzellen exprimiert. Die WB-Analysen von Mammakarzinomen zeigen eine positive Korrelation der ALCAM-Expression mit dem Östrogenrezeptorstatus (p=0,04). Bei Patientinnen, die eine taxanfreie Chemotherapie erhalten haben, ist eine hohe ALCAM-Expression (WB, Affymetrix) prädikitiv für das Ansprechen einer Chemotherapie. Der mediane mRNA-Level von ALCAM war bei Patientinnen, die während des Beobachtungszeitraums noch lebten, 4,5-fach höher als bei Patientinnen, die verstarben. Schlussfolgerung: Ein hoher ALCAM-Gehalt korreliert positiv mit dem Östrogenrezeptorstatus. Außerdem ist ALCAM ein prädiktiver Faktor für das Ansprechen einer taxanfreien Chemotherapi
A comparison of the efficacy of dimethyl sulfoxide (dmso) and synovial fluid in the prevention of peritoneal adhesions: experimental rabbit model
The Shortest Period Detached Binary White Dwarf System
We identify SDSS J010657.39-100003.3 (hereafter J0106-1000) as the shortest
period detached binary white dwarf (WD) system currently known. We targeted
J0106-1000 as part of our radial velocity program to search for companions
around known extremely low-mass (ELM, ~ 0.2 Msol) WDs using the 6.5m MMT. We
detect peak-to-peak radial velocity variations of 740 km/s with an orbital
period of 39.1 min. The mass function and optical photometry rule out a
main-sequence star companion. Follow-up high-speed photometric observations
obtained at the McDonald 2.1m telescope reveal ellipsoidal variations from the
distorted primary but no eclipses. This is the first example of a tidally
distorted WD. Modeling the lightcurve, we constrain the inclination angle of
the system to be 67 +- 13 deg. J0106-1000 contains a pair of WDs (0.17 Msol
primary + 0.43 Msol invisible secondary) at a separation of 0.32 Rsol. The two
WDs will merge in 37 Myr and most likely form a core He-burning single subdwarf
star. J0106-1000 is the shortest timescale merger system currently known. The
gravitational wave strain from J0106-1000 is at the detection limit of the
Laser Interferometer Space Antenna (LISA). However, accurate ephemeris and
orbital period measurements may enable LISA to detect J0106-1000 above the
Galactic background noise.Comment: MNRAS Letters, in pres
A Dark Spot on a Massive White Dwarf
We present the serendipitous discovery of eclipse-like events around the
massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We
selected J1529+2928 for time-series photometry based on its spectroscopic
temperature and surface gravity, which place it near the ZZ Ceti instability
strip. Instead of pulsations, we detect photometric dips from this white dwarf
every 38 minutes. Follow-up optical spectroscopy observations with Gemini
reveal no significant radial velocity variations, ruling out stellar and brown
dwarf companions. A disintegrating planet around this white dwarf cannot
explain the observed light curves in different filters. Given the short period,
the source of the photometric dips must be a dark spot that comes into view
every 38 min due to the rotation of the white dwarf. Our optical spectroscopy
does not show any evidence of Zeeman splitting of the Balmer lines, limiting
the magnetic field strength to B<70 kG. Since up to 15% of white dwarfs display
kG magnetic fields, such eclipse-like events should be common around white
dwarfs. We discuss the potential implications of this discovery on transient
surveys targeting white dwarfs, like the K2 mission and the Large Synoptic
Survey Telescope.Comment: ApJ Letters, in pres
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