21 research outputs found
A search for rapidly pulsating hot subdwarf stars in the GALEX survey
NASA's Galaxy Evolution Explorer (GALEX) provided near- and far-UV
observations for approximately 77 percent of the sky over a ten-year period;
however, the data reduction pipeline initially only released single NUV and FUV
images to the community. The recently released Python module gPhoton changes
this, allowing calibrated time-series aperture photometry to be extracted
easily from the raw GALEX data set. Here we use gPhoton to generate light
curves for all hot subdwarf B (sdB) stars that were observed by GALEX, with the
intention of identifying short-period, p-mode pulsations. We find that the
spacecraft's short visit durations, uneven gaps between visits, and dither
pattern make the detection of hot subdwarf pulsations difficult. Nonetheless,
we detect UV variations in four previously known pulsating targets and report
their UV pulsation amplitudes and frequencies. Additionally, we find that
several other sdB targets not previously known to vary show promising signals
in their periodograms. Using optical follow-up photometry with the Skynet
Robotic Telescope Network, we confirm p-mode pulsations in one of these
targets, LAMOST J082517.99+113106.3, and report it as the most recent addition
to the sdBVr class of variable stars.Comment: 11 Pages, 8 Figures, Accepted for publication in the Astrophysical
Journa
Signatures of an eruptive phase before the explosion of the peculiar core-collapse SN 2013gc
We present photometric and spectroscopic analysis of the peculiar
core-collapse SN 2013gc, spanning seven years of observations. The light curve
shows an early maximum followed by a fast decline and a phase of almost
constant luminosity. At +200 days from maximum, a brightening of 1 mag is
observed in all bands, followed by a steep linear luminosity decline after +300
d. In archival images taken between 1.5 and 2.5 years before the explosion, a
weak source is visible at the supernova location, with mag20. The
early supernova spectra show Balmer lines, with a narrow (560 km
s) P-Cygni absorption superimposed on a broad (3400 km s)
component, typical of type IIn events. Through a comparison of colour curves,
absolute light curves and spectra of SN 2013gc with a sample of supernovae IIn,
we conclude that SN 2013gc is a member of the so-called type IId subgroup. The
complex profile of the H line suggests a composite circumstellar medium
geometry, with a combination of lower velocity, spherically symmetric gas and a
more rapidly expanding bilobed feature. This circumstellar medium distribution
has been likely formed through major mass-loss events, that we directly
observed from 3 years before the explosion. The modest luminosity
( near maximum) of SN 2013gc at all phases, the very small amount
of ejected Ni (of the order of M), the major
pre-supernova stellar activity and the lack of prominent [O I] lines in
late-time spectra support a fall-back core-collapse scenario for the massive
progenitor of SN~2013gc.Comment: 20 pages, 11 figures, 8 tables, accepted by MNRA
The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125
We report on multi-wavelength observations, ranging from the X-ray to radio
wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic
observations reveal the presence of absorption lines due to O I, Si II, and C
IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in
particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days,
corresponding to a jet opening angle of ~7.0 degrees, and implying an intrinsic
GRB energy in the 1 - 10,000 keV band of around E = (6.3 - 6.9)x 10^(51) erg
(based on the fluences measured by the gamma-ray detectors of the IPN network).
GRB 070125 is among the brightest afterglows observed to date. The spectral
energy distribution implies a host extinction of Av < 0.9 mag. Two
rebrightening episodes are observed, one with excellent time coverage, showing
an increase in flux of 56% in ~8000 seconds. The evolution of the afterglow
light curve is achromatic at all times. Late-time observations of the afterglow
do not show evidence for emission from an underlying host galaxy or supernova.
Any host galaxy would be subluminous, consistent with current GRB host-galaxy
samples. Evidence for strong Mg II absorption features is not found, which is
perhaps surprising in view of the relatively high redshift of this burst and
the high likelihood for such features along GRB-selected lines of sight.Comment: 50 pages, 9 figures, 5 tables Accepted to the Astrophysical Journa
GRB Afterglows and Other Transients in the SDSS
The Sloan Digital Sky Survey (SDSS) will image one quarter of the sky centered on the northern galactic cap and produce a 3âD map of galaxies and quasars found in the sample. An additional 225 deg2 southern survey will be imaged repeatedly on varying timescales. Here we discuss both archival searches in the SDSS catalog (such as SDSS J24602.54+011318.8) and active searches with the SDSS instruments (such as for GRB 010222) for GRB afterglows and other transient objects. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87288/2/349_1.pd
Sediment geochemistry PASOM research cruise (2009) - Murray Ridge region, northern Arabian Sea
In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25 cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 ”mol/L). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters
Mapping the Milky Way: A Radio Astronomy-Directed Investigation for Lecture-Based Astro 101 Courses
The Green Bank 20-meter radio telescope integrated into the Skynet Robotic Telescope Network offers a unique opportunity to engage learners in investigations that are not possible with optical telescopes. Radio investigation of the Milky Way using the neutral hydrogen (HI) 1420.41 MHz emission line have a long history with the educators at Green Bank Observatory and through the Skynet team. The project discussed considers how best to adapt these investigations into a large-enrollment, general education, introductory college astronomy course (âAstro 101â). Astro 101 courses serve over 250,000 students nationwide each year. To conduct a class-wide investigation of the Milky Way, we first have each student collect a 60-second radio spectral scan of the HI emission line for a single portion of the galactic disk. Once this class data over a wide range of galactic longitudes is combined, the students can use simple geometry and Doppler information to determine that we live in a spiral galaxy and that we orbit the galactic center clockwise (if looking down on the Galactic North Pole). Together with archived data of the Large and Small Magellanic Clouds, a galactic rotation curve and an enclosed mass curve can be created to illustrate the âmissing massâ problem as evidence for existence of dark matter. Results from a formative assessment illustrate that this project helps students connect concepts learned in class and gain confidence in their abilities to do scientific research. Activity lecture slides and data spreadsheets are freely available