Papers

Refereed Papers in the Last Two Years

see also Papers Older Than Two Years


"KELT-24b: A 5M_jup Planet on a 5.6 day Well-aligned Orbit around the Young V = 8.3 F-star HD 93148," Rodriguez, et al., AJ, 158, 197 (Nov. 2019).

This KELT discovery is of a rather massive hot Jupiter orbiting a quite bright star, making it an interesting target for future atmospheric studies. Doppler tomography shows that the planets orbit is aligned well with the rotation of the star. The host star is relatively young (less than a billion years old) and quite hot.
 
Rodriguez Fig 4 Rodriguez Fig 8

 

"KELT-23Ab: A Hot Jupiter Transiting a Near-solar Twin Close to the TESS and JWST Continuous Viewing Zones," Johns, et al., AJ, 158, 78 (Aug. 2019).

A significantly inflated hot Jupiter (with a density of about 0.5) this newly discovered exoplanet orbits a moderately bright host star. It has one of the highest ecliptic latitudes of any known transiting exoplanets, which places it near the TESS and JWST continuous viewing zones, making it an appealing target for follow-up studies. We contributed a full-transit light curve to the discovery and characterization of this exoplanet at the Peter van Kamp Observatory at Swarthmore.
 
Johns Fig 2 Johns Fig 3 Johns Fig 8

 

"Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties (MOBSTER) - I. First-light observations of known magnetic B and A stars," David-Uraz, et al., MNRAS, 487, 304 (Jul. 2019).

Magnetic O, B, and A stars (about 10% of these spectral types have large-scale, often quite strong, magnetic fields that trap wind plasma, forming rotating magnetospheres) have numerous observational signatures that show rotational modulation. TESS which is monitoring the sky searching for exoplanets provides a rich photometric time-series dataset of rotationally modulated magnetic massive stars. The MOBSTER collaboration is systematically studying this category of stars using TESS data and associated modeling and supplemental diagnostics. In this first paper we present period measurements of 19 previously known magnetic massive stars observed in the first two TESS fields.
 
David-Uraz Fig 1 David-Uraz Fig 2 David-Uraz Fig A1

 

"Extreme resonance line profile variations in the ultraviolet spectra of NGC 1624-2: probing the giant magnetosphere of the most strongly magnetized known O-type star," David-Uraz, et al., MNRAS, 483, 2814 (Feb. 2019).

The star NGC 1624-2 has by far the strongest known magnetic field – and largest magnetosphere – of any O star. Here we present the first ultraviolet spectrscopy of this extreme magnetic O star, which show extreme variations in the C IV and Si IV doublet shapes and strengths between the high state and low state (representing different viewing angles through the magnetosphere and wind). Preliminary modeling (based on the Analytic Dynamic Magnetosphere model) shows that non-spherical wind models will be necessary to fully characterize the UV spectral properties of the star's magnetosphere and wind.
 
David-Uraz Fig 1 David-Uraz Fig 3

 

"KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-solar Twin," Labadie-Bartz, et al., ApJS, 240, 13 (Jan. 2019).

This KELT discovery is a quite massive (3.5 MJ) hot Jupiter orbiting a Sun-like star. The system my be a triple – we present an AO detection of a companion and the radial velocity curve shows a long-term trend, indicating a possible third star in the system. The system has some unusual kinematic properties in the Galaxy.
 
Labadie-Bartz Fig 9 Labadie-Bartz Fig 12 Labadie-Bartz Fig 13

 

"The KELT Follow-up Network and Transit False-positive Catalog: Pre-vetted False Positives for TESS," Collins, et al., AJ, 156, 234 (Nov. 2018).

This paper provides a comprehensive description of KELT and its Follow-Up Network (KFUN). The KELT discovery telescope has a functional resolution of several arc minutes and so follow-up with larger telescopes, having a smaller plate scale, is required and most candidates are false positives. After ten years of operation, with 20 validated exoplanet discoveries, KFUN has followed up on about 1600 candidates. This paper primarily describes the 1128 astrophysical false positives (mostly eclipsing binaries) among the bright (6 < V < 13) candidate stars.
 
Collins Fig 2 Collins Fig 3

 

"KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System," Johnson, et al., AJ, 155, 100 (Feb. 2018).

This hot Jupiter is notable for its host star's unusual metal abundances and for its presence in a triple star system. Its orbital plane is well aligned with the host star's rotation.
 
Johnson Fig 8 Johnson Fig 11 Johnson Fig 14

 

"KELT-19Ab: A P ˜ 4.6-day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion," Siverd, et al., AJ, 155, 35 (Jan. 2018).

Doppler tomography shows a nearly complete misalignment of this planet's orbit with its host star's rotation. The host star is probably a chemically peculiar Am star, while the planet has a radius nearly twice that of Jupiter's and a computed equilibrium temperature of about 2000 K.
 
Siverd Fig 7 Siverd Fig 8 Siverd Fig 13

 

"KELT-20b: A Giant Planet with a Period of P ~ 3.5 days Transiting the V ~ 7.6 Early A Star HD 185603," Lund, et al., AJ, 154, 194 (Nov. 2017).

This KELT discovery of a hot Jupiter – supported by two transit observations from Swarthmore's Peter van de Kamp Observatory – features one of the hottest and brightest host stars known. We present Doppler tomography to confirm the planetary status of the companion, though due to the host's rapid rotation, we can't measure the planet's mass.
 
Lund Fig 8 Lund Fig 9 Lund Fig 11

 


Refereed Papers Older Than Two Years


 

Selected Meeting Proceedings

Meeting and Talk Presentations are also available

"The X-ray View of OB Star Wind Structure and Dynamics," Cohen, Circumstellar Dynamics at High Resolution, Foz do Iguacu, Brazil (2012). Appears in ASPC, 464, 267 (2012).


"X-ray Spectroscopy of the O2 If* star HD 93129A," Cohen, Four Decades of Research on Massive Stars, Lac Taureau (2011). Appears in ASPC, 465, 147 (2013). Also, from the same meeting and conference proceedings, "An X-ray Survey of Colliding Wind Binaries," Gagné, Fehon, Savoy, Cartagena, Cohen, & Owocki; and "The Physical Basis of the Lx/Lbol Empirical Law for O-Star X-rays," Owocki, Sundqvist, Cohen, & Gayley.


"X-ray Spectral Diagnostics of Activity in Massive Stars," Cohen, Wollman, & Leutenegger, IAU 272: Active OB Stars: Structure, Evolution, and Mass Loss, Paris (2010). Appears in IAU Symposium No. 272, eds. Neiner, Wade, Meynet, & Peters, Cambridge University Press, p. 348 (2011).


"X-ray Spectroscopy of the Radiation-Driven Winds of Massive Stars: Line Profile and Line Ratio Diagnostics," Cohen, 16th International Conference on Atomic Processes in Plasmas, Monterey, CA (2009). Appears in AIP conf. ser. 1161, p. 132 (2009).


"Modelling, Design and Diagnostics for a Photoionised Plasma Experiment," [or ADS] Hall, Durmaz, Mancini, Bailey, Rochau, Rosenberg, Cohen, Golovkin, MacFarlane, Sherril, Abdallah, Heeter, Foord, Glenzer, & Scott, High Energy Density Laboratory Astrophysics, St. Louis (2008). Appears in Astrophysics and Space Science, 322, 117 (2009).


"X-ray Emission from O Stars," Cohen, IAU 250: Massive Stars as Cosmic Engines, Kauai, Hawaii (2007). Appears in IAU Symposium No. 250, eds. Bresolin, Crowther, & Puls, Cambridge University Press, p. 17 (2008). This is a color version, with one extra figure (and with the transcribed questions and answers that followed the talk). There is also a black-and-white version, identical to the six-page article that appears in the bound conference proceedings.


"X-rays from Magnetically Channeled Winds of OB Stars," [or ADS] Cohen, IAU 250: Massive Stars as Cosmic Engines, Kauai, Hawaii (2007). Appears in IAU Symposium No. 250, eds. Bresolin, Crowther, & Puls, Cambridge University Press, p. 577 (2008).


"Quantitative Analysis of Resolved X-ray Emission Line Profiles of O Stars," Cohen, Leutenegger, & Townsend, International Workshop on Clumping in Hot-Star Winds, University of Potsdam, Germany (2007). To appear electronically: University of Potsdam (Universitats-Verlag).


"Resonance Scattering in the X-ray Emission Line Profiles of ζ Puppis," Leutenegger, Cohen, Kahn, Owocki, & Paerels, International Workshop on Clumping in Hot-Star Winds, University of Potsdam, Germany (2007). To appear electronically: University of Potsdam (Universitats-Verlag).


"Flow Dynamics and Plasma Heating of Spheromaks in SSX," Brown, Cothran, Cohen, Horwitz ('07), & Chaplin ('07), Innovative Confinement Concepts Workshop, University of Maryland, (2007). Appears in Journal of Fusion Energy.


"Diagnostics of Disks Around Hot Stars," Cohen, Hanson, Townsend, Bjorkman, & Gagné, The Nature and Evolution of Disks Around Hot Stars, Eastern Tennessee State University, Johnson City, TN (2004). Appears in ASP Conf. Ser., 337, p. 59 (2005).


"Analysis of Doppler-Broadened X-ray Emission Line Profiles from Hot Stars," Cohen, Kramer, & Owocki, MSSL Workshop on High-Resolution X-ray Spectroscopy, Dorking, Surrey, UK, (2002). Available via cd, and on-line.


"X-rays from Hot Stars and Young Stellar Objects," Gagné, Cohen, Owocki, & ud-Doula, X-rays in Sharp Focus: Chandra Science Symposium, St. Paul, MN (2001). Appears in ASP Conf. Ser., 262, p. 31 (2002).


"EUV/X-ray Emission and the Thermal and Ionization Structure of B Star Winds," Cohen, Thermal and Ionization Aspects of Flows from Hot Stars: Observation and Theory, Tartu, Estonia, (1999). Appears in ASP Conf. Ser., 204, p. 65 (2000).


"X-ray Emission from Isolated Be Stars," Cohen, The Be Phenomenon in Early-Type Stars, IAU colloquium 175, Alicante, Spain, (1999). Appears in ASP Conf. Ser., 214, p. 156 (2000).


 

 


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David Cohen: cohen -at- astro -dot- swarthmore -dot- edu
Last modified: November 24, 2019