arXiv subjects

Yossi Shvartzvald

Publications and source records attributed to Yossi Shvartzvald.

183 records · Page 11Linked to original sources

arXiv2015

Criteria for Sample Selection to Maximize Planet Sensitivity and Yield from Space-Based Microlens Parallax Surveys

Space-based microlens parallax measurements are a powerful tool for understanding planet populations, especially their distribution throughout the Galaxy. However, if space-based observations of the microlensing events must be specifically targeted, it is crucial that microlensing events enter the parallax sample without reference to the known presence or absence of planets. Hence, it is vital to define objective criteria for selecting events where possible and to carefully consider and minimize the selection biases where not possible so that the final sample represents a controlled experiment. We present objective criteria for initiating observations and determining their cadence for a subset of events, and we define procedures for isolating subjective decision making from information about detected planets for the remainder of events. We also define procedures to resolve conflicts between subjective and objective selections. These procedures maximize planet sensitivity of the sample as a whole by allowing for planet detections even if they occur before satellite observations for objectively-selected events and by helping to trigger fruitful follow-up observations for subjectively-chosen events. This paper represents our public commitment to these procedures, which is a necessary component of enforcing objectivity on the experimental protocol.

astro-ph.EP↗

arXiv2013

Fast radio bursts may originate from nearby flaring stars

Six cases of fast radio bursts (FRBs) have recently been discovered. The FRBs are bright (~0.1 - 1 Jy) and brief (~ 1 ms) pulses of radio emission with dispersion measures (DMs) that exceed Galactic values, and hence FRBs have been interpreted to be at cosmological distances. We propose, instead, that FRBs are rare eruptions of flaring main-sequence stars within ~1 kpc. Rather than associating their excess DM with the intergalactic medium, we relate it to a blanket of coronal plasma around their host stars. We have monitored at optical bands the stars within the radio beams of three of the known FRBs. In one field, we find a bright (V=13.6 mag) variable star (0.2 mag peak-to-trough) with a main-sequence G-type spectrum and a period P = 7.8 hr, likely a W-UMa-type contact binary. Analysis of our data outside of the FRB beams indicates a 5% chance probability of finding a variable star of this brightness and amplitude within the FRB beams. We find no unusual variable stars in the other two FRB fields. Further observations are needed to investigate if similar nearby (<~ 800 pc) stars are the sources of FRBs.

astro-ph.HE↗

arXiv2011

Second-generation microlensing planet surveys: a realistic simulation

Microlensing surveys, which have discovered about a dozen extrasolar planets to date, have focused on the small minority of high-magnification lensing events, which have a high sensitivity to planet detection. In contrast, second-generation experiments, of the type that has recently begun, monitor continuously also the majority of low-magnification events. We carry out a realistic numerical simulation of such experiments. We simulate scaled, solar-like, eight-planet systems, studying a variety of physical parameters (planet frequency, scaling of the snowline with stellar mass R_snow ~ M^s), and folding in the various observational parameters (cadence, experiment duration), with sampling sequences and photometric error distributions taken from the real ongoing experiment. We quantify the dependence of detected planet yield on cadence and experiment duration, e.g., the yield is doubled when going from 3-hour to 15-minute baseline cadences, or from an 80-day-long to a 150-day-long experiment. There is a degeneracy between the snowline scaling index s and the abundance of planetary systems that can be inferred from the experiment, in the context of our scaled solar-analog model. After 4 years, the ongoing second-generation experiment will discover of the order of 50 planets, and thus will be able to determine the frequency of snowline planet occurrence to a precision of 10-30%, assuming the fraction of stars hosting such planets is between 1/3 and 1/10, and a snowline index in the range s=0.5 to 2. If most planetary systems are solar analogs, over 65% of the detected planets will be "Jupiters", five in six of the detected anomalies will be due to a single planet, and one in six will reveal two planets in a single lensing event.

astro-ph.EP↗