Browsing by Subject "quiescence"

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HST And Optical Data Reveal White Dwarf Cooling, Spin, And Periodicities In GW Librae 3-4 Years After Outburst
(2012-07) Szkody, Paula; Mukadam, Anjum S.; Gansicke, Boris T.; Henden, Arne; Sion, Edward M.; Townsley, Dean; Chote, Paul; Harmer, Diane; Harpe, Eric J.; Hermes, J. J.; Sullivan, Denis J.; Winget, D. E.; Winget, D. E.
Since the large amplitude 2007 outburstwhich heated its accreting, pulsatingwhite dwarf, the dwarf nova system GW Librae has been cooling to its quiescent temperature. Our Hubble Space Telescope ultraviolet spectra combined with ground-based optical coverage during the third and fourth year after outburst show that the fluxes and temperatures are still higher than quiescence (T = 19,700 K and 17,300 K versus 16,000 K pre-outburst for a log g = 8.7 and d = 100 pc). The K-wd of 7.6 +/- 0.8 km s(-1) determined from the C I lambda 1463 absorption line, as well as the gravitational redshift implies a white dwarf mass of 0.79 +/- 0.08 M-circle dot. The widths of the UV lines imply a white dwarf rotation velocity v sin i of 40 km s(-1) and a spin period of 209 s (for an inclination of 11 deg and a white dwarf radius of 7 x 10(8) cm). Light curves produced from the UV spectra in both years show a prominent multiplet near 290 s, with higher amplitude in the UV compared to the optical, and increased amplitude in 2011 versus 2010. As the presence of this set of periods is intermittent in the optical on weekly timescales, it is unclear how this relates to the non-radial pulsations evident during quiescence.
The Mass Of The Black Hole In XTE J1118+480
(2013-01) Khargharia, Juthika; Froning, Cynthia S.; Robinson, Edward L.; Gelino, Dawn M.; Robinson, Edward L.
We present contemporaneous, broadband, near-infrared spectroscopy (0.9-2.45 mu m) and H-band photometry of the black hole X-ray binary, XTE J1118+480. We determined the fractional dilution of the NIR ellipsoidal light curves of the donor star from other emission sources in the system by comparing the absorption features in the spectrum with field stars of known spectral type. We constrained the donor star spectral type to K7 V-M1 V and determined that the donor star contributed 54% +/- 27% of the H-band flux at the epoch of our observations. This result underscores the conclusion that the donor star cannot be assumed to be the only NIR emission source in quiescent X-ray binaries. The H-band light curve shows a double-humped asymmetric modulation with extra flux at orbital phase 0.75. The light curve was fitted with a donor star model light curve, taking into account a constant second flux component based on the dilution analysis. We also fitted models that included emission from the donor star, a constant component from the accretion disk, and a phase-variable component from the bright spot where the mass accretion stream impacts the disk. These simple models with reasonable estimates for the component physical parameters can fully account for the observed light curve, including the extra emission at phase 0.75. From our fits, we constrained the binary inclination to 68 degrees <= i <= 79 degrees. This leads to a black hole mass of 6.9 M-circle dot <= M-BH <= 8.2 M-circle dot. Long-term variations in the NIR light curve shape in XTE J1118+480 are similar to those seen in other X-ray binaries and demonstrate the presence of continued activity and variability in these systems even when in full quiescence.
miR-503 Represses Human Cell Proliferation and Directly Targets the Oncogene DDHD2 by Non-Canonical Target Pairing
(2015-02) Polioudakis, Damon; Abell, Nathan S.; Iyer, Vishwanath R.; Polioudakis, Damon; Abell, Nathan S.; Iyer, Vishwanath R.
The pathways regulating the transition of mammalian cells from quiescence to proliferation are mediated by multiple miRNAs. Despite significant improvements in our understanding of miRNA targeting, the majority of miRNA regulatory networks are still largely unknown and require experimental validation. Results: Here we identified miR-503, miR-103, and miR-494 as negative regulators of proliferation in primary human cells. We experimentally determined their genome wide target profiles using RNA-induced silencing complex (RISC) immunoprecipitations and gene expression profiling. Analysis of the genome wide target profiles revealed evidence of extensive regulation of gene expression through non-canonical target pairing by miR-503. We identified the proto-oncogene DDHD2 as a target of miR-503 that requires pairing outside of the canonical 5' seed region of miR-503, representing a novel mode of miRNA-target pairing. Further bioinformatics analysis implicated miR-503 and DDHD2 in breast cancer tumorigenesis. Conclusions: Our results provide an extensive genome wide set of targets for miR-503, miR-103, and miR-494, and suggest that miR-503 may act as a tumor suppressor in breast cancer by its direct non-canonical targeting of DDHD2.