Benjamin J. Shappee

Benjamin J. Shappee
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Benjamin J. Shappee
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Solar and Stellar Astrophysics (17)
 
Cosmology and Nongalactic Astrophysics (5)
 
High Energy Astrophysical Phenomena (3)
 
Astrophysics of Galaxies (1)
 
Instrumentation and Methods for Astrophysics (1)
 
General Relativity and Quantum Cosmology (1)
 
Earth and Planetary Astrophysics (1)

Publications Authored By Benjamin J. Shappee

Ages and masses of young stars are often estimated by comparing their luminosities and effective temperatures to pre-main sequence stellar evolution tracks, but magnetic fields and starspots complicate both the observations and evolution. To understand their influence, we study the heavily-spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from Phoenix synthetic spectra to a high-resolution near-IR IGRINS spectrum. Read More

In 2016 May, the intermediate polar FO~Aqr was detected in a low state for the first time in its observational history. We report time-resolved photometry of the system during its initial recovery from this faint state. Our data, which includes high-speed photometry with cadences of just 2 sec, shows the existence of very strong periodicities at 22. Read More

In some planet formation theories, protoplanets grow gravitationally within a young star's protoplanetary disk, a signature of which may be a localized disturbance in the disk's radial and/or vertical structure. Using time-series photometric observations by the Kilodegree Extremely Little Telescope South (KELT-South) project and the All-Sky Automated Survey for SuperNovae (ASAS-SN), combined with archival observations, we present the discovery of two extended dimming events of the young star, DM Ori. This young system faded by $\sim$1. Read More

Outbursts on young stars are usually interpreted as accretion bursts caused by instabilities in the disk or the star-disk connection. However, some protostellar outbursts may not fit into this framework. In this paper, we analyze optical and near-infrared spectra and photometry to characterize the 2015 outburst of the probable young star ASASSN-15qi. Read More

Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 128 SU UMa-type dwarf novae observed mainly during the 2015-2016 season and characterized these objects. Read More

We report the discovery and classification of SDSS~J053341.43+001434.1 (SDSS0533), an early-L dwarf first discovered during a powerful $\Delta V < -11$ magnitude flare observed as part of the ASAS-SN survey. Read More

We present late-time optical spectroscopy taken with the Large Binocular Telescope's Multi-Object Double Spectrograph, an improved ASAS-SN pre-discovery non-detection, and late-time SWIFT observations of the nearby ($d=193$ Mpc, $z=0.0436$) tidal disruption event (TDE) ASASSN-14ae. Our observations span from $\sim$20 days before to $\sim$750 days after discovery. Read More

2015Jul
Authors: Taichi Kato, Franz-Josef Hambsch, Pavol A. Dubovsky, Igor Kudzej, Berto Monard, Ian Miller, Hiroshi Itoh, Seiichiro Kiyota, Kazunari Masumoto, Daiki Fukushima, Hiroki Kinoshita, Kazuki Maeda, Jyunya Mikami, Risa Matsuda, Naoto Kojiguchi, Miho Kawabata, Megumi Takenaka, Katsura Matsumoto, Enrique de Miguel, Yutaka Maeda, Tomohito Ohshima, Keisuke Isogai, Roger D. Pickard, Arne Henden, Stella Kafka, Hidehiko Akazawa, Noritoshi Otani, Sakiko Ishibashi, Minako Ogi, Kenji Tanabe, Kazuyoshi Imamura, William Stein, Kiyoshi Kasai, Tonny Vanmunster, Peter Starr, Elena P. Pavlenko, Oksana I. Antonyuk, Kirill A. Antonyuk, Aleksei A. Sosnovskij, Nikolaj V. Pit, Julia V. Babina, Aleksandr Sklyanov, Rudolf Novak, Arto Oksanen, Shawn Dvorak, Raul Michel, Gianluca Masi, Colin Littlefield, Joseph Ulowetz, Sergey Yu. Shugarov, Polina Yu. Golysheva, Drahomir Chochol, Viktoriia Krushevska, Javier Ruiz, Tamas Tordai, Etienne Morelle, Richard Sabo, Hiroyuki Maehara, Michael Richmond, Natalia Katysheva, Kenji Hirosawa, William N. Goff, Franky Dubois, Ludwig Logie, Steve Rau, Irina B. Voloshina, Maksim V. Andreev, Kazuhiko Shiokawa, Vitaly V. Neustroev, George Sjoberg, Sergey Zharikov, Nick James, Greg Bolt, Tim Crawford, Denis Buczynski, Lewis M. Cook, Christopher S. Kochanek, Benjamin Shappee, Krzysztof Z. Stanek, Jose L. Prieto, Denis Denisenko, Hideo Nishimura, Masaru Mukai, Shizuo Kaneko, Seiji Ueda, Rod Stubbings, Masayuki Moriyama, Patrick Schmeer, Eddy Muyllaert, Jeremy Shears, Robert J. Modic, Kevin B. Paxson

Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2014-2015 season and characterized these objects. Read More

2014Jun
Affiliations: 1Kyoto U

Continuing the project described by Kato et al. (2009, PASJ, 61, S395, arXiv:0905.1757), we collected times of superhump maxima for 56 SU UMa-type dwarf novae mainly observed during the 2013-2014 season and characterized these objects. Read More

2013Oct

Continuing the project described by Kato et al. (2009a, arXiv:0905.1757), we collected times of superhump maxima for SU UMa-type dwarf novae mainly observed during the 2012-2013 season. Read More

Kozai-Lidov (KL) oscillations can accelerate compact object mergers via gravitational wave (GW) radiation by driving the inner binaries of hierarchical triples to high eccentricities. We perform direct three-body integrations of high mass ratio compact object triple systems using Fewbody including post-Newtonian terms. We find that the inner binary undergoes rapid eccentricity oscillations (REOs) on the timescale of the outer orbital period which drive it to higher eccentricities than secular theory would otherwise predict, resulting in substantially reduced merger times. Read More

We study the orbital evolution of hierarchical quadruple systems composed of two binaries on a long mutual orbit, where each binary acts as a Kozai-Lidov (KL) perturber on the other. We find that the coupling between the two binaries qualitatively changes the behavior of their KL cycles. The binaries can experience coherent eccentricity oscillations as well as excursions to very high eccentricity that occur over a much larger fraction of the parameter space than in triple systems. Read More

We measure the decay rate of the mid-IR luminosity from type Ia supernova 2011fe between six months and one year after explosion using Spitzer/IRAC observations. The fading in the 3.6 micron channel is 1. Read More

A generic prediction of the single-degenerate model for Type Ia supernovae (SNe Ia) is that a significant amount of material will be stripped from the donor star (~0.5 Msun for a giant donor and ~0.15 Msun for a main sequence donor) by the supernova ejecta. Read More

We report the discovery via radial velocity of a short-period (P = 2.430420 \pm 0.000006 days) companion to the F-type main sequence star TYC 2930-00872-1. Read More

In the single-degenerate (SD) channel of a Type Ia supernovae (SN Ia) explosion, a main-sequence (MS) donor star survives the explosion but it is stripped of mass and shock heated. An essentially unavoidable consequence of mass loss during the explosion is that the companion must have an overextended envelope after the explosion. While this has been noted previously, it has not been strongly emphasized as an inevitable consequence. Read More

Over a broad range of initial inclinations and eccentricities an appreciable fraction of hierarchical triple star systems with similar masses are essentially unaffected by the Kozai-Lidov mechanism (KM) until the primary in the central binary evolves into a compact object. Once it does, it may be much less massive than the other components in the ternary, enabling the "eccentric Kozai mechanism (EKM):" the mutual inclination between the inner and outer binary can flip signs driving the inner binary to very high eccentricity, leading to a close binary or collision. We demonstrate this "Mass-loss Induced Eccentric Kozai" (MIEK) mechanism by considering an example system and defining an ad-hoc minimal separation between the inner two members at which tidal affects become important. Read More

We accurately determine a new Cepheid distance to M101 (NGC 5457) using archival HST/ACS V and I time series photometry of two fields within the galaxy. We make a slight modification to the ISIS image subtraction package to obtain optimal differential light curves from HST data. We discovered 827 Cepheids with periods between 3 and 80 days, the largest extragalactic sample of Cepheids observed with HST by a factor of 2. Read More