146 research outputs found
High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
APOGEE has amassed the largest ever collection of multi-epoch, high-resolution (R~22,500), H-band spectra for B-type emission line (Be) stars. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the total number of known Be stars by ~6%. We focus on identification of the H-band lines and analysis of the emission peak velocity separations (v_p) and emission peak intensity ratios (V/R) of the usually double-peaked H I and non-hydrogen emission lines. H I Br11 emission is found to preferentially form in the circumstellar disks at an average distance of ~2.2 stellar radii. Increasing v_p toward the weaker Br12--Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe II emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe II and H I Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including ~16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large v_p compared to the Br11-Br20, a tracer of the inner regions of Be disks. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe II 16878, never exhibit any evidence of shell absorption, even when the H I lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra- and/or extra-species V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample
High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
APOGEE has amassed the largest ever collection of multi-epoch,
high-resolution (R~22,500), H-band spectra for B-type emission line (Be) stars.
The 128/238 APOGEE Be stars for which emission had never previously been
reported serve to increase the total number of known Be stars by ~6%. We focus
on identification of the H-band lines and analysis of the emission peak
velocity separations (v_p) and emission peak intensity ratios (V/R) of the
usually double-peaked H I and non-hydrogen emission lines. H I Br11 emission is
found to preferentially form in the circumstellar disks at an average distance
of ~2.2 stellar radii. Increasing v_p toward the weaker Br12--Br20 lines
suggests these lines are formed interior to Br11. By contrast, the observed IR
Fe II emission lines present evidence of having significantly larger formation
radii; distinctive phase lags between IR Fe II and H I Brackett emission lines
further supports that these species arise from different radii in Be disks.
Several emission lines have been identified for the first time including
~16895, a prominent feature in the spectra for almost a fifth of the sample
and, as inferred from relatively large v_p compared to the Br11-Br20, a tracer
of the inner regions of Be disks. Unlike the typical metallic lines observed
for Be stars in the optical, the H-band metallic lines, such as Fe II 16878,
never exhibit any evidence of shell absorption, even when the H I lines are
clearly shell-dominated. The first known example of a quasi-triple-peaked Br11
line profile is reported for HD 253659, one of several stars exhibiting intra-
and/or extra-species V/R and radial velocity variation within individual
spectra. Br11 profiles are presented for all discussed stars, as are full
APOGEE spectra for a portion of the sample.Comment: accepted in A
Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
We present the largest sample of flares ever compiled for a single M dwarf,
the active M4 star GJ 1243. Over 6100 individual flare events, with energies
ranging from to erg, are found in 11 months of 1-minute
cadence data from Kepler. This sample is unique for its completeness and
dynamic range. We have developed automated tools for finding flares in
short-cadence Kepler light curves, and performed extensive validation and
classification of the sample by eye. From this pristine sample of flares we
generate a median flare template. This template shows that two exponential
cooling phases are present during the white-light flare decay, providing
fundamental constraints for models of flare physics. The template is also used
as a basis function to decompose complex multi-peaked flares, allowing us to
study the energy distribution of these events. Only a small number of flare
events are not well fit by our template. We find that complex, multi-peaked
flares occur in over 80% of flares with a duration of 50 minutes or greater.
The underlying distribution of flare durations for events 10 minutes and longer
appears to follow a broken power law. Our results support the idea that
sympathetic flaring may be responsible for some complex flare events.Comment: 12 pages, 9 figures, accepted for publication in Ap
Discovery of Two Rare Rigidly Rotating Magnetosphere Stars in the APOGEE Survey
The Apache Point Observatory Galactic Evolution Experiment (APOGEE)---one of the Sloan Digital Sky Survey III programs---is using near-infrared (NIR) spectra of ~100,000 red giant branch star candidates to study the structure of the Milky Way. In the course of the survey, APOGEE also acquires spectra of hot field stars to serve as telluric calibrators for the primary science targets. We report the serendipitous discovery of two rare, fast-rotating B-stars of the sigma Ori E type among those blue field stars observed during the first year of APOGEE operations. Both of the discovered stars display the spectroscopic signatures of rigidly rotating magnetospheres (RRM) common to this class of highly magnetized (B ~ 10 kGauss) stars, increasing the number of known RRM stars by ~10%. One (HD 345439) is a main-sequence B-star with unusually strong He absorption (similar to sigma Ori E), while the other (HD 23478) fits a "He-normal" B3IV classification. We combine the APOGEE discovery spectra with other optical and NIR spectra of these two stars, and of sigma Ori E itself, to show how NIR spectroscopy can be a uniquely powerful tool for discovering more of these rare objects, which may show little/no RRM signatures in their optical spectra. We discuss the potential for further discovery of sigma Ori E type stars, as well as the implications of our discoveries for the population of these objects and insights into their origin and evolution
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
Cellular Prion Protein Expression Is Not Regulated by the Alzheimer's Amyloid Precursor Protein Intracellular Domain
There is increasing evidence of molecular and cellular links between Alzheimer's disease (AD) and prion diseases. The cellular prion protein, PrPC, modulates the post-translational processing of the AD amyloid precursor protein (APP), through its inhibition of the β-secretase BACE1, and oligomers of amyloid-β bind to PrPC which may mediate amyloid-β neurotoxicity. In addition, the APP intracellular domain (AICD), which acts as a transcriptional regulator, has been reported to control the expression of PrPC. Through the use of transgenic mice, cell culture models and manipulation of APP expression and processing, this study aimed to clarify the role of AICD in regulating PrPC. Over-expression of the three major isoforms of human APP (APP695, APP751 and APP770) in cultured neuronal and non-neuronal cells had no effect on the level of endogenous PrPC. Furthermore, analysis of brain tissue from transgenic mice over-expressing either wild type or familial AD associated mutant human APP revealed unaltered PrPC levels. Knockdown of endogenous APP expression in cells by siRNA or inhibition of γ-secretase activity also had no effect on PrPC levels. Overall, we did not detect any significant difference in the expression of PrPC in any of the cell or animal-based paradigms considered, indicating that the control of cellular PrPC levels by AICD is not as straightforward as previously suggested
Peter Pan Disks: Long-lived Accretion Disks Around Young M Stars
WISEA J080822.18-644357.3, an M star in the Carina association, exhibits
extreme infrared excess and accretion activity at an age greater than the
expected accretion disk lifetime. We consider J0808 as the prototypical example
of a class of M star accretion disks at ages Myr, which we call
``Peter Pan'' disks, since they apparently refuse to grow up. We present four
new Peter Pan disk candidates identified via the Disk Detective citizen science
project, coupled with \textit{Gaia} astrometry. We find that WISEA
J044634.16-262756.1 and WISEA J094900.65-713803.1 both exhibit significant
infrared excess after accounting for nearby stars within the 2MASS beams. The
J0446 system has likelihood of Columba membership. The J0949 system
shows likelihood of Carina membership. We present new GMOS optical
spectra of all four objects, showing possible accretion signatures on all four
stars. We present ground-based and \textit{TESS} lightcurves of J0808 and 2MASS
J0501-4337, including a large flare and aperiodic dipping activity on J0808,
and strong periodicity on J0501. We find Pa and Br emission
indicating ongoing accretion in near-IR spectroscopy of J0808. Using observed
characteristics of these systems, we discuss mechanisms that lead to accretion
disks at ages Myr, and find that these objects most plausibly
represent long-lived CO-poor primordial disks, or ``hybrid'' disks, exhibiting
both debris- and primordial-disk features. The question remains: why have
gas-rich disks persisted so long around these particular stars?Comment: 25 pages, 17 figures. Accepted for publication in the Astrophysical
Journa
Epigenetic Regulation of Fatty Acid Amide Hydrolase in Alzheimer Disease
OBJECTIVE: Alzheimer disease (AD) is a progressive, degenerative and irreversible neurological disorder with few therapies available. In search for new potential targets, increasing evidence suggests a role for the endocannabinoid system (ECS) in the regulation of neurodegenerative processes. METHODS: We have studied the gene expression status and the epigenetic regulation of ECS components in peripheral blood mononuclear cells (PBMCs) of subjects with late-onset AD (LOAD) and age-matched controls (CT). RESULTS: We found an increase in fatty acid amide hydrolase (faah) gene expression in LOAD subjects (2.30 ± 0.48) when compared to CT (1.00 ± 0.14; *p<0.05) and no changes in the mRNA levels of any other gene of ECS elements. Consistently, we also observed in LOAD subjects an increase in FAAH protein levels (CT: 0.75 ± 0.04; LOAD: 1.11 ± 0.15; *p<0.05) and activity (pmol/min per mg protein CT: 103.80 ± 8.73; LOAD: 125.10 ± 4.00; *p<0.05), as well as a reduction in DNA methylation at faah gene promoter (CT: 55.90 ± 4.60%; LOAD: 41.20 ± 4.90%; *p<0.05). CONCLUSIONS: Present findings suggest the involvement of FAAH in the pathogenesis of AD, highlighting the importance of epigenetic mechanisms in enzyme regulation; they also point to FAAH as a new potential biomarker for AD in easily accessible peripheral cells
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