Papers by Stephanie Wortel-London
American Journal of Physics, 2007
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American Journal of Physics, 2009
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American Journal of Physics, 2008
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The Arecibo Legacy Fast ALFA (ALFALFA) project is an ongoing high sensitivity HI line survey with... more The Arecibo Legacy Fast ALFA (ALFALFA) project is an ongoing high sensitivity HI line survey with the 305m Arecibo telescope that will cover 7000 square degrees of sky and is expected to detect some 20,000 HI sources (Giovanelli et al. 2005, AJ in press, astro-ph/0508301). ALFALFA will make major contributions to the understanding of the structure and evolution of galaxies in the local Universe. In July 2005 an Undergraduate Research Workshop was held at Union College, Schenectady (see poster by Koopmann et al.). Participants included 14 undergraduate students, 2 graduate students, and 9 faculty members from 7 universities, in addition to the Director of the Arecibo Observatory Visitor Center. In preparation for the meeting, the students worked as a team in preparing and submitting an observing proposal to the Observatory, thus experiencing the rigorous process of matching science goals to instrumentation and other realities of the time allocation process. In addition to a mini-course on science and technical issues, students engaged in an observing session with the Arecibo telescope, which was carried out remotely and interactively from the lecture room at Union College. The region observed included a nearby loose group of galaxies, LGG 362, dominated by NGC 5363/5364. The group is an example of an intermediate galaxy density environment. As part of the workshop, the data were processed and the scientific analysis started. This poster presents the results of those observations and analysis. This research was supported by the National Astronomy and Ionosphere Center, which is operated by Cornell University under a management agreement with the National Science Foundation, and partially by NSF/AST-0307661, NSF/AST-0435697 and a Brinson Foundation grant. JA and CAP gratefully acknowledge the Arecibo Observatory and the Louis Stokes Alliance for Minority Participation at the UPR for assistance for this research.
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Astronomy & Astrophysics, 2006
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and ... more The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was R = 12.0, which represents the most luminous quasar state thus far observed (M_B ~ -31.4). In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm the
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American Journal of Physics, 2009
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American Journal of Physics, 2007
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American Journal of Physics, 2008
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A radial velocity (RV) survey to detect central stars in binary systems was carried out between 2... more A radial velocity (RV) survey to detect central stars in binary systems was carried out between 2002 and 2004. De Marco et al. (2004) reported that 10 out of 11 monitored stars exhibited strong RV variability, but periods were not detected. Since other mechanisms, such as wind variability, can cause apparent RV variations, we monitored 4 of the 10 RV-variable stars at echelle resolutions to determine the origin of the variability. Although RV changes are confirmed for all four stars, none of them can be ascribed to binarity at this time. However, only for IC4593 is wind variability able to explain most (though not all) spectral variability. For BD+332642, no wind and no pulsations appear to be the origin of the RV changes. Finally, M1-77 and M2-54, both known to be irregular photometric variables, exhibit dramatic RV and line shape variability of the hydrogen and HeI absorption lines, as well as large RV variability of weaker lines, which do not change in shape. There is no satisfactory explanation of this variability, though a combination of wind variability and pulsations is still the best guess at what makes these stars so variable. We suggest that luminous central stars are ill suited to detect spectroscopic binaries, because winds (and possibly pulsations) are pervasive and would mask even strong periodicities. It it likely that a sample of intrinsically faint central stars would more readily yield binary information.
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A radial velocity (RV) survey to detect central stars in binary systems was carried out between 2... more A radial velocity (RV) survey to detect central stars in binary systems was carried out between 2002 and 2004. De Marco et al. (2004) reported that 10 out of 11 monitored stars exhibited strong RV variability, but periods were not detected. Since other mechanisms, such as wind variability, can cause apparent RV variations, we monitored 4 of the 10 RV-variable stars at echelle resolutions to determine the origin of the variability. Although RV changes are confirmed for all four stars, none of them can be ascribed to binarity at this time. However, only for IC4593 is wind variability able to explain most (though not all) spectral variability. For BD+332642, no wind and no pulsations appear to be the origin of the RV changes. Finally, M1-77 and M2-54, both known to be irregular photometric variables, exhibit dramatic RV and line shape variability of the hydrogen and HeI absorption lines, as well as large RV variability of weaker lines, which do not change in shape. There is no satisfactory explanation of this variability, though a combination of wind variability and pulsations is still the best guess at what makes these stars so variable. We suggest that luminous central stars are ill suited to detect spectroscopic binaries, because winds (and possibly pulsations) are pervasive and would mask even strong periodicities. It it likely that a sample of intrinsically faint central stars would more readily yield binary information.
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Papers by Stephanie Wortel-London