Physical Sciences and Mathematics Commons^™

Acurate Low-Mass Stellar Models Of Koi-126, Gregory A. Feiden, Brian Chaboyer, Aaron Dotter

Dartmouth Scholarship

The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. (2011) appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the …

Discovery Of A Bright, Extremely Low Mass White Dwarf In A Close Double Degenerate System, S. Vennes, J. R. Thorstensen, A. Kawka, P. Németh, J. N. Skinner

Dartmouth Scholarship

We report the discovery of a bright (V ~ 13.7), extremely low-mass white dwarf in a close double degenerate system. We originally selected GALEX J171708.5+675712 for spectroscopic follow-up among a group of white dwarf candidates in an ultraviolet-optical reduced proper-motion diagram. The new white dwarf has a mass of 0.18 M_solar and is the primary component of a close double degenerate system (P=0.246137 d, K_1 = 288 km/s) comprising a fainter white dwarf secondary with M_2 ~ 0.9 M_solar. Light curves phased with the orbital ephemeris show evidence of relativistic beaming and weaker ellipsoidal variations. The light curves also reveal …

Laboratory Astrophysics: Using Ebit Measurements To Interpret High Resolution Spectra From Celestial Sources, Carey Scott, Joshua Thompson, N. Hell, Greg V. Brown

STAR Program Research Presentations

Astrophysicists use radiation to investigate the physics controlling a variety of celestial sources, including stellar atmospheres, black holes, and binary systems. By measuring the spectrum of the emitted radiation, astrophysicists can determine a source’s temperature and composition. Accurate atomic data are needed for reliably interpreting these spectra. Here we present an overview of how LLNL’s EBIT facility is used to put the atomic data on sound footing for use by the high energy astrophysics community.

The Variable Quiescent X-Ray Emission Of The Neutron Star Transient Xte J1701-462, Joel K. Fridriksson, Jeroen Homan, Rudy Wijnands, Edward M. Cackett, Diego Altamirano, Nathalie Degenaar, Edward F. Brown, Mariano Méndez, Tomaso M. Belloni

Physics and Astronomy Faculty Research Publications

We present the results of continued monitoring of the quiescent neutron star low-mass X-ray binary XTE J1701-462 with Chandra and Swift. A new Chandra observation from 2010 October extends our tracking of the neutron star surface temperature from ≃ 800 days to ≃ 1160 days since the end of an exceptionally luminous 19 month outburst. This observation indicates that the neutron star crust may still be slowly cooling toward thermal equilibrium with the core; another observation further into quiescence is needed to verify this. The shape of the overall cooling curve is consistent with that of a broken power law, …

Quiescent X-Ray Variability From The Neutron Star Transient Aql X-1, E. M. Cackett, J. K. Fridriksson, J. Homan, J. M. Miller, R. Wijnands

Physics and Astronomy Faculty Research Publications

A number of studies have revealed variability from neutron star low-mass X-ray binaries during quiescence. Such variability is not well characterized, or understood, but may be a common property that has been missed due to lack of multiple observations. One such source where variability has been observed is Aql X-1. Here, we analyse 14 Chandra and XMM-Newton observations of Aql X-1 in quiescence, covering a period of approximately 2 yr. There is clear variability between the epochs, with the most striking feature being a flare-like increase in the flux by a factor of 5. Spectral fitting is inconclusive as to …

The Cataclysmic Variable Sdss J1507+52: An Eclipsing Period Bouncer In The Galactic Halo, Helena Uthas, Christian Knigge, Knox S. Long, Joseph Patterson, John Thorstensen

Dartmouth Scholarship

SDSS J1507+52 is an eclipsing cataclysmic variable (CV) consisting of a cool, non-radially pulsating white dwarf and an unusually small substellar secondary. The system has a high space velocity and a very short orbital period of about 67 min, well below the usual minimum period for CVs. To explain the existence of this peculiar system, two theories have been proposed. One suggests that SDSS J1507+52 was formed from a detached white dwarf-brown dwarf binary. The other theory proposes that the system is a member of the Galactic halo population.

Here, we present the ultraviolet (UV) spectroscopy of SDSS J1507+52 obtained …

Sdss J162520.29+120308.7 – A New Su Ursae Majoris Star In The Period Gap, A. Olech, E. De Miguel, M. Otulakowska, J. R. Thorstensen

Dartmouth Scholarship

We report results of an extensive world-wide observing campaign devoted to the recently discovered dwarf nova SDSS J162520.29+120308.7 (SDSS J1625). The data were obtained during the July 2010 eruption of the star and in August and September 2010 when the object was in quiescence.

A Study Of Carbon Features In Type Ia Supernova Spectra, Jerod T. Parrent, R. C. Thomas, Robert A. Fesen, G. H. Marion

Dartmouth Scholarship

One of the major differences between various explosion scenarios of Type Ia supernovae (SNe Ia) is the remaining amount of unburned (C+O) material and its velocity distribution within the expanding ejecta. While oxygen absorption features are not uncommon in the spectra of SNe Ia before maximum light, the presence of strong carbon absorption has been reported only in a minority of objects, typically during the pre-maximum phase. The reported low frequency of carbon detections may be due to low signal-to-noise data, low abundance of unburned material, line blending between C II 6580 and Si II 6355, ejecta temperature differences, asymmetrical …

Further X-Ray Observations Of Exo 0748-676 In Quiescence: Evidence For A Cooling Neutron Star Crust, N. Degenaar, M. T. Wolff, P. S. Ray, K. S. Wood, J. Homan, W. H. G. Lewin, P. G. Jonker, E. M. Cackett, J. M. Miller, E. F. Brown, R. Wijnands

Physics and Astronomy Faculty Research Publications

In late 2008, the quasi-persistent neutron star X-ray transient and eclipsing binary EXO 0748-676 started a transition from outburst to quiescence, after it actively accreted for more than 24 yr. In a previous work, we discussed Chandra and Swift observations obtained during the first 5 months of this transition. Here, we report on further X-ray observations of EXO 0748-676, extending the quiescent monitoring to 1.6 yr. Chandra and XMM-Newton data reveal quiescent X-ray spectra composed of a soft, thermal component that is well fitted by a neutron star atmosphere model. An additional hard power-law tail is detected that changes non-monotonically …

A Fast X-Ray Disk Wind In The Transient Pulsar Igr J17480-2446 In Terzan 5, Jon M. Miller, Dipankar Maitra, Edward M. Cackett, Sudip Bhattacharyya, Tod E. Strohmayer

Physics and Astronomy Faculty Research Publications

Accretion disk winds are revealed in Chandra gratings spectra of black holes. The winds are hot and highly ionized (typically composed of He-like and H-like charge states) and show modest blueshifts. Similar line spectra are sometimes seen in "dipping" low-mass X-ray binaries (LMXBs), which are likely viewed edge-on; however, that absorption is tied to structures in the outer disk, and blueshifts are not typically observed. Here, we report the detection of blueshifted He-like Fe XXV (3100 ± 400 km s^-1) and H-like Fe XXVI (1000 ± 200 km s^-1) absorption lines in a Chandra/HETG spectrum of …

High-Quality Broadband Bvri Photometry Of Benchmark Open Clusters, Michael Deloss Joner

Theses and Dissertations

Photometric techniques are often used to observe stars and it can be demonstrated that fundamental stellar properties can be observationally determined using calibrated sets of photometric data. Many of the most powerful techniques utilized to calibrate stellar photometry employ the use of stars in clusters since the individual stars are believed to have many common properties such as age, composition, and approximate distance. Broadband photometric Johnson/Cousins BVRI observations are presented for several nearby open clusters. The new photometry has been tested for consistency relative to archival work and shown to be both accurate and precise. The careful use of a …

Spitzer 24Μm Survey For Dust Disks Around Hot White Dwarfs, You-Hua Chu, Kate Y.L. Su, Jana Bilikova, Robert A. Gruendl, Orsola De Marco, Martin A. Guerrero, Adria Updike, Kevin Volk, Thomas Rauch

Arts & Sciences Faculty Publications

No abstract provided.