Search Publications
Radiative Transfer Effects on Doppler Measurements as Sources of Surface Effects in Sunspot Seismology
Scherrer, P. H.; Wachter, R.; Sankarasubramanian, K. +1 more
We show that the use of Doppler shifts of Zeeman-sensitive spectral lines to observe waves in sunspots is subject to measurement-specific phase shifts arising from (1) the altered height range of spectral line formation and the propagating character of p-mode waves in penumbrae and (2) Zeeman broadening and splitting. We also show that these phase…
Modeling Spitzer Observations of VV Ser. I. The Circumstellar Disk of a UX Orionis Star
van Dishoeck, Ewine F.; Dullemond, Cornelis P.; Pontoppidan, Klaus M. +5 more
We present mid-infrared Spitzer IRS spectra of the UX Orionis star VV Ser, combined with interferometric and spectroscopic data from the literature covering UV to submillimeter wavelengths. The full set of data are modeled by an axisymmetric Monte Carlo radiative transfer code to test the prediction of Dullemond et al. that disks around UX Orionis…
The Survey of Nearby Nuclei with the Space Telescope Imaging Spectrograph: Emission-Line Nuclei at Hubble Space Telescope Resolution
Filippenko, Alexei V.; Ho, Luis C.; Shields, Joseph C. +6 more
We present results from a program of optical spectroscopy for 23 nearby galaxies with emission-line nuclei. This investigation takes advantage of the spatial resolution of the Hubble Space Telescope to study the structure and energetics of the central ~10-20 pc, and the resulting data have value for quantifying central black hole masses, star form…
An Alternative Interpretation of the Relationship between the Inferred Open Solar Flux and the Interplanetary Magnetic Field
Riley, Pete
Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that i…
Differences in the AGN Populations of Groups and Clusters: Clues to AGN Evolution
Shen, Yue; Raychaudhury, Somak; Mulchaey, John S. +2 more
We combine optical and X-ray data for eight low-redshift (z~0.06) poor groups of galaxies from the XI (XMM-IMACS) Groups Project to study the AGN population in the group environment. Among ~140 group members, we identify five AGNs based on their optical emission lines. None of these optically selected AGNs are detected by XMM-Newton. One additiona…
A Spitzer IRAC Census of the Asymptotic Giant Branch Populations in Local Group Dwarfs. I. WLM
Skillman, Evan D.; Gehrz, Robert D.; Woodward, Charles E. +2 more
We present Spitzer IRAC observations at 3.6 and 4.5 µm along with optical data from the Local Group Galaxies Survey to investigate the evolved stellar population of the Local Group dwarf irregular galaxy WLM. These observations provide a nearly complete census of the AGB stars. We find that 39% of the infrared-detected AGB stars are not dete…
Dressing a Naked Quasar: Star Formation and Active Galactic Nucleus Feedback in HE 0450-2958
Feain, Ilana J.; Ekers, Ronald D.; Papadopoulos, Padelis P. +1 more
We present Australia Telescope Compact Array radio continuum observations of the quasar/galaxy system HE 0450-2958. An asymmetric triple linear morphology is observed, with the central radio component coincident with the quasar core and a second radio component associated with a companion galaxy at a projected distance of 7 kpc from the quasar. Th…
X-Ray-Emitting Ejecta of Supernova Remnant N132D
Reynolds, Stephen P.; Borkowski, Kazimierz J.; Hendrick, Sean P.
The brightest supernova remnant in the Magellanic Clouds, N132D, belongs to the rare class of oxygen-rich remnants, about a dozen objects that show optical emission from pure heavy-element ejecta. They originate in explosions of massive stars that produce large amounts of O, although only a tiny fraction of that O is found to emit at optical wavel…
Joint Hα and X-Ray Observations of Massive X-Ray Binaries. III. The Be X-Ray Binaries HDE 245770 = A0535+26 and X Persei
Gies, D. R.; Grundstrom, E. D.; Boyajian, T. S. +9 more
We present results from an Hα monitoring campaign of the Be X-ray binary systems HDE 245770 = A0535+26 and X Per. We use the Hα equivalent widths together with adopted values of the Be star effective temperature, disk inclination, and disk outer boundary to determine the half-maximum emission radius of the disk as a function of time. The observati…
High-Resolution X-Ray Spectroscopy of the Ultracompact LMXB Pulsar 4U 1626-67
Chakrabarty, Deepto; Schulz, Norbert S.; Cottam, Jean +2 more
We report results from four recent observations of the ultracompact LMXB pulsar 4U 1626-67. These observations obtained high-resolution X-ray spectra with Chandra HETGS and XMM RGS, allowing us to study in detail the prominent Ne and O emission-line complexes. The observations were spaced over a period of 3 yr, enabling us to monitor the line regi…