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Selected Works

Todd Hillwig

Articles 1 - 6 of 6

Full-Text Articles in Physical Sciences and Mathematics

Binary Central Stars Of Planetary Nebulae Discovered Through Photometric Variability. V. The Central Stars Of Hatr 7 And Eso 330-9, Todd Hillwig, David J. Frew, Nicole Reindl, Hannah Rotter, Andrew Webb, Steve Margheim Dec 2016

Binary Central Stars Of Planetary Nebulae Discovered Through Photometric Variability. V. The Central Stars Of Hatr 7 And Eso 330-9, Todd Hillwig, David J. Frew, Nicole Reindl, Hannah Rotter, Andrew Webb, Steve Margheim

Todd Hillwig

We find the central stars (CSs) of the planetary nebulae (PNe) HaTr7 and ESO330-9 to be close-binary systems. Both have orbital periods of less than half a day and contain an irradiated cool companion to the hot CS. We provide light curves, spectra, radial velocity curves, orbital periods, and binary modeling results for both systems. The binary modeling leads to system parameters, or ranges of allowed parameters for each system. We find that for the CS of HaTr7 we need to use limb-darkening values for the cool companion …

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Binary Central Stars Of Planetary Nebulae Discovered Through Photometric Variability. Iii. The Central Star Of Abell 65, Todd Hillwig, David J. Frew, Melissa Louie, Orsola De Marco, Sam Schaub Jul 2016

Binary Central Stars Of Planetary Nebulae Discovered Through Photometric Variability. Iii. The Central Star Of Abell 65, Todd Hillwig, David J. Frew, Melissa Louie, Orsola De Marco, Sam Schaub

Todd Hillwig

A growing number of close binary stars are being discovered among central stars of planetary nebulae. Recent and ongoing surveys are finding new systems and contributing to our knowledge of the evolution of close binary systems. The push to find more systems was largely based on early discoveries which suggested that 10%–15% of all central stars are close binaries. One goal of this series of papers is confirmation and classification of these systems as close binaries and determination of binary system parameters. Here we provide time-resolved multi-wavelength photometry of the central star of Abell 65 as well as further analysis …

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Multiwavelength Observations Of The Ss 433 Jets, Herman L. Marshall, Claude R. Canizares, Todd Hillwig, Amy Mioduszewski, Michael Rupen, Norbert S. Schulz, Michael Nowak, Sebastian Heinz Sep 2013

Multiwavelength Observations Of The Ss 433 Jets, Herman L. Marshall, Claude R. Canizares, Todd Hillwig, Amy Mioduszewski, Michael Rupen, Norbert S. Schulz, Michael Nowak, Sebastian Heinz

Todd Hillwig

We present observations of the SS 433 jets using the Chandra High Energy Transmission Grating Spectrometer with contemporaneous optical and Very Long Baseline Array observations. The X-ray and optical emission line regions are found to be related but not coincident as the optical line emission persists for days while the X-ray emission lines fade in less than 5000 s. The line Doppler shifts from the optical and X-ray lines match well, indicating that they are less than 3 × 1014 cm apart. The jet Doppler shifts show aperiodic variations that could result from shocks in interactions with the local …

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Radial Velocities Of Galactic O-Type Sars. Ii. Single-Lined Spectroscopic Binaries, S. J. Williams, D. R. Gies, Todd Hillwig, M. V. Mcswain, W. Huang Dec 2012

Radial Velocities Of Galactic O-Type Sars. Ii. Single-Lined Spectroscopic Binaries, S. J. Williams, D. R. Gies, Todd Hillwig, M. V. Mcswain, W. Huang

Todd Hillwig

We report on new radial velocity measurements of massive stars that are either suspected binaries or lacking prior observations. This is part of a survey to identify and characterize spectroscopic binaries among O-type stars with the goal of comparing the binary fraction of field and runaway stars with those in clusters and associations. We present orbits for HDE 308813, HD 152147, HD 164536, BD−16◦4826, and HDE 229232, Galactic O-type stars exhibiting single-lined spectroscopic variation. By fitting model spectra to our observed spectra, we obtain estimates for effective temperature, surface gravity, and rotational velocity. We compute …

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Ic 4663: The First Unambiguous [Wn] Wolf–Rayet Central Star Of A Planetary Nebula, B. Miszalski, P. A. Crowther, O. De Marco, J. Koppen, A. F. J. Moffat, Agnes Acker, Todd Hillwig May 2012

Ic 4663: The First Unambiguous [Wn] Wolf–Rayet Central Star Of A Planetary Nebula, B. Miszalski, P. A. Crowther, O. De Marco, J. Koppen, A. F. J. Moffat, Agnes Acker, Todd Hillwig

Todd Hillwig

We report on the serendipitous discovery of the first central star of a planetary nebula (PN) that mimics the helium- and nitrogen-rich WN sequence of massive Wolf–Rayet (WR) stars. The central star of IC 4663 (PN G346.2−08.2) is dominated by broad He II and N V emission lines which correspond to a [WN3] spectral type. Unlike previous [WN] candidates, the surrounding nebula is unambiguously a PN. At an assumed distance of 3.5 kpc, corre- sponding to a stellar luminosity of 4000 L⊙, the V = 16.9 mag central star remains 4–6 mag fainter than the average …

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Radial Velocities Of Galactic O-Type Stars. I. Short-Term Constant Velocity Stars, S. J. Williams, D. R. Gies, Todd Hillwig, M. V. Mcswain, W. Huang Sep 2011

Radial Velocities Of Galactic O-Type Stars. I. Short-Term Constant Velocity Stars, S. J. Williams, D. R. Gies, Todd Hillwig, M. V. Mcswain, W. Huang

Todd Hillwig

We present radial velocities for 18 Galactic O-type stars. These stars display small radial velocity scatter over timescales of one to two weeks. Some of them are long-period binaries while others are probably single stars. By fitting model spectra to our observed spectra we obtain estimates for effective temperature, log g, rotational velocity, and average radial velocity for each target. 

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