Lawrence Alan Molnar

Superhump timing in SU Ursae Majoris systems : implications of the data for the precessing disk model

The most current data are tabulated for the orbital period, superhump period, and mass ratio in SU Ursae Majoris type variables to test models of the superhump timing mechanism. Contrary to earlier reports, the correlation between the superhump period excess and the orbital period is not significant. However, the correlation between the superhump period excess and the mass ratio is significant at the 4.7 σ level. This correlation was predicted by the Whitehurst model which explains superhumps as periodic enhancements of tidal dissipation in an eccentric, precessing accretion disk

The small binary asteroid (939) Isberga

In understanding the composition and internal structure of asteroids, their density is perhaps the most diagnostic quantity. We aim here at characterizing the surface composition, mutual orbit, size, mass, and density of the small main-belt binary asteroid (939) Isberga. For that, we conduct a suite of multi-technique observations, including optical lightcurves over many epochs, near-infrared spectroscopy, and interferometry in the thermal infrared. We develop a simple geometric model of binary systems to analyze the interferometric data in combination with the results of the lightcurve modeling. From spectroscopy, we classify Ibserga as a Sq-type asteroid, consistent with the albedo of View the MathML source0.14-0.06+0.09 (all uncertainties are reported as 3-σ range) we determine (average albedo of S-types is 0.197 ± 0.153, see Pravec et al. (Pravec et al. [2012]. Icarus 221, 365–387). Lightcurve analysis reveals that the mutual orbit has a period of 26.6304 ± 0.0001 h, is close to circular (eccentricity lower than 0.1), and has pole coordinates within 7° of (225°, +86°) in Ecliptic J2000, implying a low obliquity of View the MathML source1.5-1.5+6.0deg. The combined analysis of lightcurves and interferometric data allows us to determine the dimension of the system and we find volume-equivalent diameters of View the MathML source12.4-1.2+2.5km and View the MathML source3.6-0.3+0.7km for Isberga and its satellite, circling each other on a 33 km wide orbit. Their density is assumed equal and found to be View the MathML source2.91-2.01+1.72gcm-3, lower than that of the associated ordinary chondrite meteorites, suggesting the presence of some macroporosity, but typical of S-types of the same size range (Carry [2012]. Planet. Space Sci. 73, 98–118). The present study is the first direct measurement of the size of a small main-belt binary. Although the interferometric observations of Isberga are at the edge of MIDI capabilities, the method described here is applicable to others suites of instruments (e.g., LBT, ALMA).

Prediction of a Red Nova Outburst in KIC 9832227

We present the first identification of a candidate precursor for an imminent red nova. Our prediction is based on the example of the precursor to the red nova V1309 Sco, which was retrospectively found to be a contact binary with an exponentially decreasing period. We explore the use of this distinctive timing signature to identify precursors, developing the observational and analysis steps needed. We estimate that our Galaxy has roughly 1-10 observable precursors. Specifically, we lay out the observational case for KIC 9832227, which we identified as a tentative candidate two years ago (Molnar et al. 2015, AAS Meeting Abstracts 415.05). Orbital timing over the past two years has followed the tentative exponential fit. As of late 2015, the period time derivative went beyond the range found in other systems (dP/dt < 1x10^{-8}), a necessary criterion for a serious candidate. We estimate time of merger is the year 2022.2(7). Double absorption line spectra confirm directly the 0.458 d light curve period is a contact binary system and yield a mass ratio m_B/m_A = 0.228(3). Closer analysis of the Kepler timing data shows evidence of a component C with orbital period P_C = 590(8) days and m_C x sin i_C = 0.11 solar masses. An alternative interpretation of the long term timing trend, light travel time delay due to orbit around a distant component D, is ruled out by the spectroscopic data for any nondegenerate star. Additional measurements are needed to test further the merging hypothesis and to utilize fully this fortuitous opportunity.

Interpretation of the period derivative of Cygnus X-3

The time derivative of the X-ray period of Cyg X-3 has been accurately measured, and is confirmed by various satellite observations. The present results are consistent with a degenerate secondary with a mass from 0.0004-0.05 solar masses. The most probable mechanism for driving the period change is found to be either that the system is evolving toward an unstable mass transfer regime or that the orbit of a close third body serves as a sink for angular momentum. 18 references.