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Variability Of Optical Counterparts In The Chandra Galactic Bulge Survey, C. T. Britt, R. I. Hynes, C. B. Johnson, A. Baldwin, P. G. Jonker, G. Nelemans, M. A.P. Torres, T. Maccarone, D. Steeghs, S. Greiss, C. Heinke, C. G. Bassa, A. Collazzi, A. Villar, M. Gabb, L. Gossen
Variability Of Optical Counterparts In The Chandra Galactic Bulge Survey, C. T. Britt, R. I. Hynes, C. B. Johnson, A. Baldwin, P. G. Jonker, G. Nelemans, M. A.P. Torres, T. Maccarone, D. Steeghs, S. Greiss, C. Heinke, C. G. Bassa, A. Collazzi, A. Villar, M. Gabb, L. Gossen
Faculty Publications
We present optical light curves of variable stars consistent with the positions of X-ray sources identified with the Chandra X-ray Observatory for the Chandra Galactic Bulge Survey (GBS). Using data from the Mosaic-II instrument on the Blanco 4 m Telescope at CTIO, we gathered time-resolved photometric data on timescales from ∼2 hr to 8 days over the 3/4 of the X-ray survey containing sources from the initial GBS catalog. Among the light curve morphologies we identify are flickering in interacting binaries, eclipsing sources, dwarf nova outbursts, ellipsoidal variations, long period variables, spotted stars, and flare stars. Eighty-seven percent of X-ray …
The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King
The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King
Jeremy R King
In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow ”Li-peak” at approximately the correct temperature. However, with more detailed studies into J37s abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars. Thanks to the specific predictions made about the behaviour of Be abundances, (the most …
Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King
Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King
Jeremy R King
The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual pattern of photospheric abundances, including an order of magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the …
Post-Outburst Observations Of V1647 Orionis: Detection Of A Brief Warm Molecular Outflow, Sean D. Brittain, Terrence W. Rettig, Theodore Simon, Dinshaw S. Balsara, David Tilley, Erika Gibb, Kenneth H. Hinkle
Post-Outburst Observations Of V1647 Orionis: Detection Of A Brief Warm Molecular Outflow, Sean D. Brittain, Terrence W. Rettig, Theodore Simon, Dinshaw S. Balsara, David Tilley, Erika Gibb, Kenneth H. Hinkle
Sean D Brittain
We present new observations of the fundamental rovibrational CO spectrum of V1647 Ori, the young star whose recent outburst illuminated McNeil's Nebula. Previous spectra, acquired during outburst in 2004 February and July, had shown the CO emission lines to be broad and centrally peaked, similar to the CO spectrum of a typical classical T Tauri star. In this Letter, we present CO spectra acquired shortly after the luminosity of the source returned to its pre-outburst level (2006 February) and roughly 1 year later (2006 December and 2007 February). The spectrum taken in 2006 February revealed blueshifted CO absorption lines superimposed …
Near-Infrared Spectroscopic Study Of V1647 Ori, Sean D. Brittain, T W. Rettig, Theodore Simon, Erika L. Gibb, Joseph Liskowsky
Near-Infrared Spectroscopic Study Of V1647 Ori, Sean D. Brittain, T W. Rettig, Theodore Simon, Erika L. Gibb, Joseph Liskowsky
Sean D Brittain
We present new high-resolution infrared echelle spectra of V1647 Ori, the young star that illuminates McNeil's nebula. From the start, V1647 Ori has been an enigmatic source that has defied classification, in some ways resembling eruptive stars of the FUor class and in other respects the EXor variables. V1647 Ori underwent an outburst in 2003 before fading back to its pre-outburst brightness in 2006. In 2008, it underwent a new outburst. In this paper we present high-resolution K-band and M-band spectra from the W. M. Keck Observatory that were acquired during the 2008 outburst. We compare the spectra to spectra …
A Spectro-Astrometric Measurement Of Brackett Gamma Emission In Herbig Ae/Be Stars, Thomas S. Rice, Sean D. Brittain
A Spectro-Astrometric Measurement Of Brackett Gamma Emission In Herbig Ae/Be Stars, Thomas S. Rice, Sean D. Brittain
Sean D Brittain
In T Tauri stars, the Brackett gamma line strength is a reliable indicator of accretion luminosity. Among intermediate mass young stars, Herbig Ae stars also show this correlation, but in Herbig Be stars the Brgamma line flux significantly overpredicts accretion luminosity. This Brgamma excess in Herbig Be stars is thought to arise from a spatially extended outflow. Using commissioning data from the LUCIFER spectrograph on the 8.4-meter Large Binocular Telescope (LBT), we present a spectro-astrometric study of two Herbig Ae/Be stars, the HAe star MWC480 and the HBe star HD 259431. In both stars, an extended Brgamma source can be …
Warm Gas In The Inner Disks Around Young Intermediate-Mass Stars, Sean D. Brittain, Theodore Simon, Joan R. Najita, Terrence W. Rettig
Warm Gas In The Inner Disks Around Young Intermediate-Mass Stars, Sean D. Brittain, Theodore Simon, Joan R. Najita, Terrence W. Rettig
Sean D Brittain
The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K- and M-band spectroscopy of 14 intermediate-mass young stars. In sources that have optically thick inner disks, i.e., E(K-L)>1, our detection rate of the rovibrational CO transitions is 100%, and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the rovibrational CO transitions from HD 141569. In this case, we show that the …
Co Emission In The Inner Disk Around Young Intermediate-Mass Stars, Matt L. Stevans, Sean D. Brittain
Co Emission In The Inner Disk Around Young Intermediate-Mass Stars, Matt L. Stevans, Sean D. Brittain
Sean D Brittain
We present observations that indicate viscous heating contributes significantly to the surface heating of the inner disk region (0.1-5 AU) around young intermediate-mass stars, Herbig AeBe stars, when the inner disk is optically thick. Brgamma flux is known to scale with accretion rate around young stars. We find a trend between Brgamma and CO emissivity, a tracer 1, 500 K gas in the gaseous atmospheres of less evolved inner disk regions in a sample of 25 Herbig AeBe stars, the higher mass analog of T Tauri stars. Evolved Herbig circumstellar disks do not follow this trend as closely. A thermal …
Accretion Variability Of Herbig Ae/Be Stars Observed By X-Shooter Hd 31648 And Hd 163296, I Mendigutia, Sean D. Brittain, C Eiroa, G Meeus, B Montesinos, A Mora, J Muzerolle, R D. Oudmaijer, E Rigliaco
Accretion Variability Of Herbig Ae/Be Stars Observed By X-Shooter Hd 31648 And Hd 163296, I Mendigutia, Sean D. Brittain, C Eiroa, G Meeus, B Montesinos, A Mora, J Muzerolle, R D. Oudmaijer, E Rigliaco
Sean D Brittain
This work presents X-Shooter/Very Large Telescope spectra of the prototypical, isolated Herbig Ae stars HD 31648 (MWC 480) and HD 163296 over five epochs separated by timescales ranging from days to months. Each spectrum spans over a wide wavelength range covering from 310 to 2475 nm. We have monitored the continuum excess in the Balmer region of the spectra and the luminosity of 12 ultraviolet, optical, and near-infrared spectral lines that are commonly used as accretion tracers for T Tauri stars. The observed strengths of the Balmer excesses have been reproduced from a magnetospheric accretion shock model, providing a mean …
Measuring The Stellar Accretion Rates Of Herbig Ae/Be Stars, Brian Donehew, Sean D. Brittain
Measuring The Stellar Accretion Rates Of Herbig Ae/Be Stars, Brian Donehew, Sean D. Brittain
Sean D Brittain
The accretion rate of young stars is a fundamental characteristic of these systems.While accretion onto T Tauri stars has been studied extensively, little work has been done on measuring the accretion rate of their intermediate-mass analogs, the Herbig Ae/Be stars. Measuring the stellar accretion rate of Herbig Ae/Bes is not straightforward both because of the dearth of metal absorption lines available for veiling measurements and the intrinsic brightness of Herbig Ae/Be stars at ultraviolet wavelengths where the brightness of the accretion shock peaks. Alternative approaches to measuring the accretion rate of young stars by measuring the luminosity of proxies such …
Multiwavelength Observations Of Young Stars And Their Circumstellar Disks, David A. Principe
Multiwavelength Observations Of Young Stars And Their Circumstellar Disks, David A. Principe
Theses
Observational studies of star and planet formation represent a fundamental means to understand the origins of exoplanetary systems and our own solar system. In this dissertation I present a multiwavelength approach to study a wide range of stages of the evolution of protostars and pre-main sequence (pre-MS) stars. I have investigated, via an infrared and multi-epoch X-ray study of the L1630 dark cloud, whether and how X-ray variability in young stellar objects is related to protostellar evolutionary state. Among a subsample of 52 X-ray-emitting young stars in L1630, I find that the earliest stages of young stellar evolution show the …
Characterizing The Quiescent X-Ray Variability Of The Black Hole Low-Mass X-Ray Binary V404 Cyg, F Bernardini, E. M. Cackett
Characterizing The Quiescent X-Ray Variability Of The Black Hole Low-Mass X-Ray Binary V404 Cyg, F Bernardini, E. M. Cackett
Physics and Astronomy Faculty Research Publications
We conducted the first long-term (75 d) X-ray monitoring of the black hole low-mass X-ray binary V404 Cyg, with the goal of understanding and characterizing its variability during quiescence. The X-ray light curve of V404 Cyg shows several flares on time-scales of hours with a count rate change of a factor of about 5–8. The root-mean-square variability isFvar = 57.0 ± 3.2 per cent. The first-order structure function is consistent with both a power spectrum of index −1 (flicker noise), or with a power spectrum of index 0 (white noise), implying that the light curve is variable on …
Multi-Wavelength Coverage Of State Transitions In The New Black Hole X-Ray Binary Swift J1910.2-0546, N. Degenaar, D. Maitra, E. M. Cackett, M. T. Reynolds, J M. Miller, R. C. Reis, A L. King, K. Gültekin, C D. Bailyn, M M. Buxton, R K. D Macdonald, A. C. Fabian, D B. Fox, E. S. Rykoff
Multi-Wavelength Coverage Of State Transitions In The New Black Hole X-Ray Binary Swift J1910.2-0546, N. Degenaar, D. Maitra, E. M. Cackett, M. T. Reynolds, J M. Miller, R. C. Reis, A L. King, K. Gültekin, C D. Bailyn, M M. Buxton, R K. D Macdonald, A. C. Fabian, D B. Fox, E. S. Rykoff
Physics and Astronomy Faculty Research Publications
Understanding howblack holes accrete and supply feedback to their environment is one of the outstanding challenges of modern astrophysics. Swift J1910.2–0546 is a candidate black hole low-mass X-ray binary that was discovered in 2012 when it entered an accretion outburst. To investigate the binary configuration and the accretion morphology, we monitored the evolution of the outburst for ≃3 months at X-ray, UV, optical (B,V,R,I), and near-infrared (J,H,K) wavelengths using Swift and SMARTS. The source evolved from a hard to a soft X-ray spectral state with a relatively cold accretion disk that peaked at ≃0.5 keV. A Chandra/HETG spectrum obtained during …
The Galactic Bulge Survey: Completion Of The X-Ray Survey Observations, Peter G. Jonker, Manuel A.P. Torres, Robert I. Hynes, Thomas J. Maccarone, Danny Steeghs, Sandra Greiss, Christopher T. Britt, Jianfeng Wu, Christopher B. Johnson, Gijs Nelemans, Craig Heinke
The Galactic Bulge Survey: Completion Of The X-Ray Survey Observations, Peter G. Jonker, Manuel A.P. Torres, Robert I. Hynes, Thomas J. Maccarone, Danny Steeghs, Sandra Greiss, Christopher T. Britt, Jianfeng Wu, Christopher B. Johnson, Gijs Nelemans, Craig Heinke
Faculty Publications
We provide the Chandra source list for the last quarter of the area covered by the Galactic Bulge Survey (GBS). The GBS targets two strips of 6° × 1° (12 square degrees in total), one above (1° < b < 2°) and one below (-2° < b < -1°) the Galactic plane in the direction of the Galactic center at X-ray, optical, and near-infrared wavelengths. For the X-ray part of the survey we use 2 ks per Chandra pointing. We find 424 X-ray sources in the 63 Chandra observations on which we report here. These sources are in addition to the 1216 X-ray sources discovered in the first part of the GBS survey described previously. We discuss the characteristics and the X-ray variability of the brightest of the sources as well as the radio properties from existing radio surveys. We point out an interesting asymmetry in the number of X-ray sources as a function of their Galactic l and b coordinates which is probably caused by differences in average extinction toward the different parts of the GBS survey area. © 2014. The American Astronomical Society. All rights reserved..
Multiwavelength Observations Of Swift J1753.5-0127, Cynthia S. Froning, Thomas J. Maccarone, Kevin France, Lisa Winter, Edward L. Robinson, Robert I. Hynes, Fraser Lewis
Multiwavelength Observations Of Swift J1753.5-0127, Cynthia S. Froning, Thomas J. Maccarone, Kevin France, Lisa Winter, Edward L. Robinson, Robert I. Hynes, Fraser Lewis
Faculty Publications
We present contemporaneous X-ray, ultraviolet (UV), optical, and near-infrared observations of the black hole binary system Swift J1753.5-0127 acquired in 2012 October. The UV observations, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, are the first UV spectra of this system. The dereddened UV spectrum is characterized by a smooth, blue continuum and broad emission lines of C IV and He II. The system was stable in the UV to <10% during our observations. We estimated the interstellar reddening by fitting the 2175 Å absorption feature and fit the interstellar absorption profile of Lyα to directly measure the neutral hydrogen column density along the line of sight. By comparing the UV continuum flux to steady-state thin accretion disk models, we determined upper limits on the distance to the system as a function of black hole mass. The continuum is well fit with disk models dominated by viscous heating rather than irradiation. The broadband spectral energy distribution shows the system has declined at all wavelengths since previous broadband observations in 2005 and 2007. If we assume that the UV emission is dominated by the accretion disk, the inner radius of the disk must be truncated at radii above the innermost stable circular orbit to be consistent with the X-ray flux, requiring significant mass loss from outflows and/or energy loss via advection into the black hole to maintain energy balance. © 2014. The American Astronomical Society. All rights reserved.
Ysovar: Mid-Ir Variability In The Star Forming Region Lynds 1688, H. M. Gunther, A. M. Cody, K. R. Covey, L. A. Hillenbrand, P. Plavchan, K. Poppenhaeger, L. M. Rebull, J. R. Stauffer, S. J. Wolk, L. Allen, A. Bayo, R. A. Gutermuth, J. L. Hora, H.Y.A. Meng, M. Morales-Calderon, J. R. Parks, Inseok Song
Ysovar: Mid-Ir Variability In The Star Forming Region Lynds 1688, H. M. Gunther, A. M. Cody, K. R. Covey, L. A. Hillenbrand, P. Plavchan, K. Poppenhaeger, L. M. Rebull, J. R. Stauffer, S. J. Wolk, L. Allen, A. Bayo, R. A. Gutermuth, J. L. Hora, H.Y.A. Meng, M. Morales-Calderon, J. R. Parks, Inseok Song
Robert A. Gutermuth
The emission from young stellar objects (YSOs) in the mid-infrared (mid-IR) is dominated by the inner rim of their circumstellar disks. We present IR data from the Young Stellar Object VARiability (YSOVAR) survey of ~800 objects in the direction of the Lynds 1688 (L1688) star-forming region over four visibility windows spanning 1.6 yr using the Spitzer Space Telescope in its warm mission phase. Among all light curves, 57 sources are cluster members identified based on their spectral energy distribution and X-ray emission. Almost all cluster members show significant variability. The amplitude of the variability is larger in more embedded YSOs. …
How Mangrove Forests Adjust To Rising Sea Level, Ken W. Krauss, Karen L. Mckee, Catherine E. Lovelock, Donald R. Cahoon, Neil Saintilan, Ruth Reef, Luzhen Chen
How Mangrove Forests Adjust To Rising Sea Level, Ken W. Krauss, Karen L. Mckee, Catherine E. Lovelock, Donald R. Cahoon, Neil Saintilan, Ruth Reef, Luzhen Chen
United States Geological Survey: Staff Publications
Mangroves are among the most well described and widely studied wetland communities in the world. The greatest threats to mangrove persistence are deforestation and other anthropogenic disturbances that can compromise habitat stability and resilience to sea-level rise. To persist, mangrove ecosystems must adjust to rising sea level by building vertically or become submerged. Mangroves may directly or indirectly influence soil accretion processes through the production and accumulation of organic matter, as well as the trapping and retention of mineral sediment. In this review, we provide a general overview of research on mangrove elevation dynamics, emphasizing the role of the vegetation …