Holly A. Sheets

The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar-Type Stars

We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg (P = 2.35 days). A third star is visible in the spectrum, and the system is a hierarchical triple. We combine the radial velocities for the three stars, times of eclipse, and intermediate astrometric data from the Hipparcos mission (abscissa residuals) to establish the elements of the outer orbit, which is eccentric and has a period of 15.8 yr. We determine accurate values for the masses, radii, and effective temperatures of the binary components: MAa = 1.282 ± 0.015 M☉, RAa = 1.615 ± 0.017 R☉, and T = 6180 ± 100 K for the primary (star Aa), and MAb = 0.9315 ± 0.0068 M☉, RAb = 0.974 ± 0.020 R☉, and T = 5300 ± 150 K for the secondary (Ab). The mass of the tertiary is determined to be MB = 0.925 ± 0.036 M☉ and its effective temperature is T = 5670 ± 150 K. Current stellar evolution models agree well with the properties of the primary but show a very large discrepancy in the radius of the secondary, in the sense that the predicted values are ~10% smaller than observed (a ~5 σ effect). In addition, the temperature is cooler than predicted, by some 200 K. These discrepancies are quite remarkable given that the star is only 7% less massive than the Sun, the calibration point of all stellar models. We identify the chromospheric activity as the likely cause of the effect. Inactive stars agree very well with the models, while active ones such as V1061 Cyg Ab appear systematically too large and too cool.

STATISTICAL ECLIPSES OF CLOSE-IN KEPLER SUB-SATURNS

We present a method to detect small atmospheric signals in Keplers planet candidate light curves by averaging light curves for multiple candidates with similar orbital and physical characteristics. Our statistical method allows us to measure unbiased physical properties of Keplers planet candidates, even for candidates whose individual signal-to-noise precludes the detection of their secondary eclipse. We detect a secondary eclipse depth of 3.83 +1.10/-1.11 ppm for a group of 31 sub-Saturn (R 10 ppm). Including Kepler-10b in this group increases the depth to 5.08 +0.71/-0.72 ppm. For a control group with (R_p/a)^2 < 1 ppm, we find a depth of 0.36 +/- 0.37 ppm, consistent with no detection. We also analyze the light curve of Kepler-10b and find an eclipse depth of 7.08 +/- 1.06 ppm. If the eclipses are due solely to reflected light, this corresponds to a geometric albedo of 0.22 +/- 0.06 for our group of close-in sub-Saturns, 0.37 +/- 0.05 if including Kepler-10b in the group, and 0.60 +/- 0.09 for Kepler-10b alone. Including a thermal emission model does not change the geometric albedo appreciably, assuming the Bond albedo is 2/3 the geometric albedo. Our result for Kepler-10b is consistent with previous works. Our result for close-in sub-Saturns shows that Kepler-10b is unusually reflective, but our analysis is consistent with the results of Demory (2014) for super-Earths. Our results also indicate that hot Neptunes are typically more reflective than hot Jupiters.

Rapid Oscillations in Cataclysmic Variables. XVII. 1RXS J070407 + 262501

We present a study of the recently discovered intermediate polar 1RXS J070407 + 262501, distinctive for its large-amplitude pulsed signal at P = 480 s. Radial velocities indicate an orbital period of 0.1821(2) days, and the light curves suggest 0.18208(6) days. Time-series photometry shows a precise spin period of 480.6700(4) s, decreasing at a rate of 0.096(9) ms yr-1: i.e., on a time scale =2.5×106 yr. The light curves also appear to show a mysterious signal at P = 0.263 days, which could possibly signify the presence of a superhump in this magnetic cataclysmic variable.

Average Albedos of Close-in Super-Earths and Super-Neptunes from Statistical Analysis of Long-cadence Kepler Secondary Eclipse Data

We present the results of our work to determine the average albedo for small, close-in planets in the Kepler candidate catalog. We have adapted our method of averaging short-cadence light curves of multiple Kepler planet candidates to long-cadence data, in order to detect an average albedo for the group of candidates. Long-cadence data exist for many more candidates than the short-cadence data, and so we separate the candidates into smaller radius bins than in our previous work: 1–2 , 2–4 , and 4–6 . We find that, on average, all three groups appear darker than suggested by the short-cadence results, but not as dark as many hot Jupiters. The average geometric albedos for the three groups are 0.11 ± 0.06, 0.05 ± 0.04, and 0.23 ± 0.11, respectively, for the case where heat is uniformly distributed about the planet. If heat redistribution is inefficient, the albedos are even lower, since there will be a greater thermal contribution to the total light from the planet. We confirm that newly identified false-positive Kepler Object of Interest (KOI) 1662.01 is indeed an eclipsing binary at twice the period listed in the planet candidate catalog. We also newly identify planet candidate KOI 4351.01 as an eclipsing binary, and we report a secondary eclipse measurement for Kepler-4b (KOI 7.01) of ~7.50 ppm at a phase of ~0.7, indicating that the planet is on an eccentric orbit.

A Spectroscopic Study of HL Canis Majoris

We present optical spectroscopy of the dwarf nova HL Canis Majoris over a span of 4 years. The observations were made during standstill, outburst, and quiescence. We determine an orbital period of 0.2167867 ± 0.0000017 days, based on radial velocities determined from Hα, Hβ, and He i λ 5876 emission. We also present equivalent widths of the spectral features in outburst and in quiescence.