arXiv subjects

David Polishook

Publications and source records attributed to David Polishook.

43 records · Page 3Linked to original sources

arXiv2011

Spin vector and shape of (6070) Rheinland and their implications

Main belt asteroids (6070) Rheinland and (54827) 2001NQ8 belong to a small population of couples of bodies which reside on very similar heliocentric orbits. Vokrouhlicky & Nesvorny (2008, AJ 136, 280) promoted a term "asteroid pairs", pointing out their common origin within the past tens to hundreds of ky. Previous attempts to reconstruct the initial configuration of Rheinland and 2001NQ8 at the time of their separation have led to the prediction that Rheinland's rotation should be retrograde. Here we report extensive photometric observations of this asteroid and use the lightcurve inversion technique to directly determine its rotation state and shape. We confirm the retrograde sense of rotation of Rheinland, with obliquity value constrained to be >= 140 deg. The ecliptic longitude of the pole position is not well constrained as yet. The asymmetric behavior of Rheinland's lightcurve reflects a sharp, near-planar edge in our convex shape representation of this asteroid. Our calibrated observations in the red filter also allow us to determine $H_R = 13.68\pm 0.05$ and $G = 0.31\pm 0.05$ values of the H-G system. With the characteristic color index $V-R = 0.49\pm 0.05$ for the S-type asteroids, we thus obtain $H = 14.17\pm 0.07$ for the absolute magnitude of (6070) Rheinland. This a significantly larger value than previously obtained from analysis of the astrometric survey observations. We next use the obliquity constraint for Rheinland to eliminate some degree of uncertainty in the past propagation of its orbit. This is because the sign of the past secular change of its semimajor axis due to the Yarkovsky effect is now constrained. Determination of the rotation state of the secondary component, asteroid (54827) 2001NQ8, is the key element in further constraining the age of the pair and its formation process.

astro-ph.EP↗

arXiv2011

The Progenitor of Supernova 2011dh/PTF11eon in Messier 51

We have identified a luminous star at the position of supernova (SN) 2011dh/PTF11eon, in pre-SN archival, multi-band images of the nearby, nearly face-on galaxy Messier 51 (M51) obtained by the Hubble Space Telescope with the Advanced Camera for Surveys. This identification has been confirmed, to the highest available astrometric precision, using a Keck-II adaptive-optics image. The available early-time spectra and photometry indicate that the SN is a stripped-envelope, core-collapse Type IIb, with a more compact progenitor (radius ~1e11 cm) than was the case for the well-studied SN IIb 1993J. We infer that the extinction to SN 2011dh and its progenitor arises from a low Galactic foreground contribution, and that the SN environment is of roughly solar metallicity. The detected object has absolute magnitude M_V^0 ~ -7.7 and effective temperature ~6000 K. The star's radius, ~1e13 cm, is more extended than what has been inferred for the SN progenitor. We speculate that the detected star is either an unrelated star very near the position of the actual progenitor, or, more likely, the progenitor's companion in a mass-transfer binary system. The position of the detected star in a Hertzsprung-Russell diagram is consistent with an initial mass of 17--19 Msun. The light of this star could easily conceal, even in the ultraviolet, the presence of a stripped, compact, very hot (~1e5 K), nitrogen-rich Wolf-Rayet star progenitor.

astro-ph.CO↗

arXiv2011

SN2010jp (PTF10aaxi): A Jet-Driven Type II Supernova

We present photometry and spectroscopy of the peculiar TypeII supernova (SN) 2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a relatively low peak absolute magnitude of only -15.9, and a low radioactive decay luminosity at late times that suggests a nickel mass below 0.003 $M_{\odot}$. Spectra of SN2010jp display an unprecedented triple-peaked H$α$ line profile, showing: (1) a narrow (800 km/s) central component that suggests shock interaction with dense CSM; (2) high-velocity blue and red emission features centered at -12600 and +15400 km/s; and (3) broad wings extending from -22000 to +25000 km/s. These features persist during 100 days after explosion. We propose that this line profile indicates a bipolar jet-driven explosion, with the central component produced by normal SN ejecta and CSM interaction at mid latitudes, while the high-velocity bumps and broad line wings arise in a nonrelativistic bipolar jet. Two variations of the jet interpretation seem plausible: (1) A fast jet mixes 56Ni to high velocities in polar zones of the H-rich envelope, or (2) the reverse shock in the jet produces blue and red bumps in Balmer lines when a jet interacts with dense CSM. Jet-driven SNeII are predicted for collapsars resulting from a wide range of initial masses above 25 $M_{\odot}$ at sub-solar metallicity. This seems consistent with the SN host environment, which is either an extremely low-luminosity dwarf galaxy or very remote parts of an interacting pair of star-forming galaxies. It also seems consistent with the low 56Ni mass that may accompany black hole formation. We speculate that the jet survives to produce observable signatures because the star's H envelope was mostly stripped away by previous eruptive mass loss.

astro-ph.HE↗

arXiv2011

PTF11eon/SN2011dh: Discovery of a Type IIb Supernova From a Compact Progenitor in the Nearby Galaxy M51

On May 31, 2011 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras, as well as by the Palomar Transient Factory (PTF) survey, and rapidly confirmed it to be a Type II supernova. Our early light curve and spectroscopy indicates that PTF11eon resulted from the explosion of a relatively compact progenitor star as evidenced by the rapid shock-breakout cooling seen in the light curve, the relatively low temperature in early-time spectra and the prompt appearance of low-ionization spectral features. The spectra of PTF11eon are dominated by H lines out to day 10 after explosion, but initial signs of He appear to be present. Assuming that He lines continue to develop in the near future, this SN is likely a member of the cIIb (compact IIb; Chevalier and Soderberg 2010) class, with progenitor radius larger than that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor. Our data imply that the object identified in pre-explosion Hubble Space Telescope images at the SN location is possibly a companion to the progenitor or a blended source, and not the progenitor star itself, as its radius (~10^13 cm) would be highly inconsistent with constraints from our post-explosion photometric and spectroscopic data.

astro-ph.CO↗

arXiv2011

A study of asteroid pole-latitude distribution based on an extended set of shape models derived by the lightcurve inversion method

Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population. We use sparse photometry from selected observatories from the AstDyS database, either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. The addition of new models increases the total number of models derived by the lightcurve inversion method to ~200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D < 30 km) is clustered towards ecliptic poles and can be explained by the YORP thermal effect while the latitude distribution of larger asteroids (D > 60 km) exhibits an evident excess of prograde rotators, probably of primordial origin.

astro-ph.EP↗

arXiv2008

The Centurion 18 telescope of the Wise Observatory

We describe the second telescope of the Wise Observatory, a 0.46-m Centurion 18 (C18) installed in 2005, which enhances significantly the observing possibilities. The telescope operates from a small dome and is equipped with a large-format CCD camera. In the last two years this telescope was intensively used in a variety of monitoring projects. The operation of the C18 is now automatic, requiring only start-up at the beginning of a night and close-down at dawn. The observations are mostly performed remotely from the Tel Aviv campus or even from the observer's home. The entire facility was erected for a component cost of about 70k$ and a labor investment of a total of one man-year. We describe three types of projects undertaken with this new facility: the measurement of asteroid light variability with the purpose of determining physical parameters and binarity, the following-up of transiting extrasolar planets, and the study of AGN variability. The successful implementation of the C18 demonstrates the viability of small telescopes in an age of huge light-collectors, provided the operation of such facilities is very efficient.

astro-ph↗

arXiv2006

Many binaries among NEAs

The number of binary asteroids in the near-Earth region might be significantly higher than expected. While Bottke and Melosh (1996) suggested that about 15% of the NEAs are binaries, as indicated from the frequency of double craters, and Pravec and Harris (2000) suggested that half of the fast-rotating NEAs are binaries, our recent study of Aten NEA lightcurves shows that the fraction of binary NEAs might be even higher than 50%. We found two asteroids with asynchronous binary characteristics such as two additive periods and fast rotation of the primary fragment. We also identified three asteroids with synchronous binary characteristics such as amplitude higher than one magnitude, U-shaped lightcurve maxima and V-shaped lightcurve minima. These five binaries were detected out of a sample of eight asteroids observed, implying a 63% binarity frequency. Confirmation of this high binary population requires the study of a larger representative sample. However, any mitigation program that requires the deflection or demise of a potential impactor will have to factor in the possibility that the target is a binary or multiple asteroid system.

astro-ph↗