Search Publications
Episodic mass loss in binary evolution to the Wolf-Rayet phase: Keck and HST proper motions of RY Scuti's nebula
Filippenko, Alexei V.; Smith, Nathan; Gehrz, Robert D. +4 more
Binary mass transfer via -Roche lobe overflow (RLOF) is a key channel for producing stripped-envelope Wolf-Rayet (WR) stars and may be critical to account for Type Ib/c supernova progenitors. RY Scuti is an extremely rare example of a massive binary star caught in this brief but important phase. Its unusual toroidal nebula indicates equatorial mas…
Twelve-hour spikes from the Crab Pevatron
Walter, R.; Ferrigno, C.; Balbo, M. +1 more
Aims: The
Methods: We divide the available data into three different sets, corres…
Identification of a Wide, Low-Mass Multiple System Containing the Brown Dwarf 2MASS J0850359+105716
Burgasser, Adam J.; Faherty, Jacqueline K.; Bochanski, John J. +3 more
We report our discovery of NLTT 20346 as an M5+M6 companion system to the tight binary (or triple) L dwarf 2MASS J0850359+105716. This nearby (~31 pc), widely separated (~7700 AU) quadruple system was identified through a cross-match of proper motion catalogs. Follow-up imaging and spectroscopy of NLTT 20346 revealed it to be a magnetically active…
The Far-ultraviolet "Continuum" in Protoplanetary Disk Systems. II. Carbon Monoxide Fourth Positive Emission and Absorption
Herczeg, Gregory J.; Valenti, Jeff A.; Harper, Graham M. +21 more
We exploit the high sensitivity and moderate spectral resolution of the Hubble Space Telescope Cosmic Origins Spectrograph to detect far-ultraviolet (UV) spectral features of carbon monoxide (CO) present in the inner regions of protoplanetary disks for the first time. We present spectra of the classical T Tauri stars HN Tau, RECX-11, and V4046 Sgr…
Comparison of a statistical model for magnetic islands in large current layers with Hall MHD simulations and Cluster FTE observations
Hwang, K. -J.; Drake, J. F.; Swisdak, M. +1 more
Magnetic islands have been observed in long current layers for various space plasmas, including the magnetopause and solar corona. In previous work exploring these magnetic islands, a statistical model was developed that described their formation, growth, convection, and coalescence in very large systems, for which simulations prove inadequate. An…
Discovery of Strong Iron Kα Emitting Compton Thick Quasars at z = 2.5 and 2.9
Daddi, E.; Alexander, D. M.; Fiore, F. +3 more
We report the detection of the 6.4 keV iron Kα emission line in two infrared-luminous, massive, star-forming BzK galaxies at z = 2.578 and z = 2.90 in the CDF-S. The Chandra 4 Ms spectra of BzK 4892 and BzK 8608 show a reflection-dominated continuum with strong iron lines, with rest-frame equivalent widths EW ~ 2.3 keV and 1.2 keV, respectively, d…
Dynamics and plasma properties of an X-ray jet from SUMER, EIS, XRT, and EUVI A & B simultaneous observations
Madjarska, M. S.
Context. Small-scale transient phenomena in the quiet Sun are believed to play an important role in coronal heating and solar wind generation. One of them, called “X-ray jet”, is the subject of our study.
Aims: We intend to investigate the dynamics, evolution, and physical properties of this phenomenon.
Methods: We combine multi-instrume…
Low abundance, strong features: window-dressing crystalline forsterite in the disk wall of HD 100546
Waters, L. B. F. M.; Dominik, C.; Henning, Th. +10 more
Context. Forsterite is one of the crystalline dust species that is often observed in protoplanetary disks and solar system comets. Being absent in the interstellar medium, it must be produced during the disk lifetime. It can therefore serve as a tracer of dust processing and disk evolution, which can lead to a better understanding of the physical …
The Effect of Helium-enhanced Stellar Populations on the Ultraviolet-upturn Phenomenon of Early-type Galaxies
Chung, Chul; Yoon, Suk-Jin; Lee, Young-Wook
Recent observations and modeling of globular clusters (GCs) with multiple populations strongly indicate the presence of super-helium-rich subpopulations in old stellar systems. Motivated by this, we have constructed new population synthesis models with and without helium-enhanced subpopulations to investigate their impact on the UV-upturn phenomen…
Chandra X-ray spectroscopy of the very early O supergiant HD 93129A: constraints on wind shocks and the mass-loss rate
Leutenegger, Maurice A.; Cohen, David H.; Sundqvist, Jon O. +5 more
We present an analysis of both the resolved X-ray emission-line profiles and the broad-band X-ray spectrum of the O2 If* star HD 93129A, measured with the Chandra High Energy Transmission Grating Spectrometer (HETGS). This star is among the earliest and most massive stars in the Galaxy, and provides a test of the embedded wind-shock scenario in a …