arXiv subjects

Tyler G. Ellis

Publications and source records attributed to Tyler G. Ellis.

4 recordsLinked to original sources

arXiv2021

Directly Determined Properties of HD 97658 from Interferometric Observations

We conducted interferometric observations with the CHARA Array of transiting super-Earth host HD 97658 and measured its limb-darkened angular diameter to be $θ_{\text{LD}}=0.314\pm0.004$ mas. The combination of the angular diameter with the Gaia EDR3 parallax value with zero-point correction ($π=46.412\pm0.022$ mas, $d=21.546\pm0.011$ pc) yields a physical radius of $R_\star=0.728\pm0.008$ $R_\odot$. We also measured the bolometric flux of the star to be $F_\text{bol}=2.42\pm 0.05\times 10^{-8}$erg s$^{-1}$ cm$^{-2}$, which, together with angular size, allows a measurement of the effective temperature $T_{\text{eff}}=5212\pm43$ K. Our directly determined physical stellar properties are in good agreement with previous estimates derived from spectroscopy. We used our measurements in combination with stellar evolutionary models and properties of the transit of HD 97658 b to determine the mass and age of HD 97658 as well as constrain the properties of the planet. Our results and our analysis of the TESS lightcurve on the planet (TOI-1821) corroborate previous studies of this system with tighter uncertainties.

astro-ph.SR↗

arXiv2018

The KELT Follow-Up Network and Transit False Positive Catalog: Pre-vetted False Positives for TESS

The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey for transiting planets orbiting bright stars for over ten years. The KELT images have a pixel scale of ~23"/pixel---very similar to that of NASA's Transiting Exoplanet Survey Satellite (TESS)---as well as a large point spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3'. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with higher spatial resolution, cadence, and photometric precision than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1,600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ~450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1,128 bright stars (6<V<10) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observations. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS.

astro-ph.EP↗

arXiv2018

The First Post-Kepler Brightness Dips of KIC 8462852

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process.

astro-ph.SR↗

arXiv2016

Remote Operations and Nightly Automation of The Red Buttes Observatory

We have implemented upgrades to the University of Wyoming's Red Buttes Observatory (RBO) to allow remote and autonomous operations using the 0.6 m telescope. Detailed descriptions of hardware and software components provide sufficient information to guide upgrading similarly designed telescopes. We also give a thorough description of the automated and remote operation modes with intent to inform the construction of routines elsewhere. Because the upgrades were largely driven by the intent to perform exoplanet transit photometry, we discuss how this science informed the automation process. A sample exoplanet transit observation serves to demonstrate RBO's capability to perform precision photometry. The successful upgrades have equipped a legacy observatory for a new generation of automated and rapid-response observations.

astro-ph.IM↗