The New Frontier: Galactic-Scale Star FormationCalzetti, D.; Kennicutt, R. C.
doi: 10.1086/605617pmid: N/A
The arena of investigation of star formation and its scaling laws is slowly, but consistently, shifting from the realm of luminous galaxies to that of faint ones and to subgalactic regions, as existing and new facilities enable investigators to probe regions of the combined parameter space of surface brightness, wavelength, and angular resolution that were inaccessible until a few years ago. We summarize what has been accomplished, and what remain as challenges in the field of galactic-scale star formation.
Hubble Space Telescope STIS Spectroscopy of the Peculiar Nova-Like Variables BK Lyn, V751 Cygni, and V380 OphZellem, Robert; Hollon, Nicholas; Ballouz, Ronald-Louis; Sion, Edward M.; Godon, Patrick; Gänsicke, Boris T.; Long, Knox
doi: 10.1086/605547pmid: N/A
We obtained Hubble STIS spectra of three nova-like variables: V751 Cygni, V380 Oph, and—the only confirmed nova-like variable known to be below the period gap—BK Lyn. In all three systems, the spectra were taken during high optical brightness state, and a luminous accretion disk dominates their far-ultraviolet (FUV) light. We assessed a lower limit of the distances by applying the infrared photometric method of Knigge. Within the limitations imposed by the poorly known system parameters (such as the inclination, white dwarf mass, and the applicability of steady state accretion disks) we obtained satisfactory fits to BK Lyn using optically thick accretion disk models with an accretion rate of for a white dwarf mass of Mwd = 1.2M⊙ and for Mwd = 0.4M⊙. However, for the VY Scl-type nova-like variable V751 Cygni and for the SW Sex star V380 Oph, we are unable to obtain satisfactory synthetic spectral fits to the high state FUV spectra using optically thick steady state accretion disk models. The lack of FUV spectra information down to the Lyman limit hinders the extraction of information about the accreting white dwarf during the high states of these nova-like systems.
Spitzer Space Telescope Observations of the Nucleus of Comet 103P/Hartley 2Lisse, C. M.; Fernandez, Y. R.; Reach, W. T.; Bauer, J. M.; A’Hearn, M. F.; Farnham, T. L.; Groussin, O.; Belton, M. J.; Meech, K. J.; Snodgrass, C. D.
doi: 10.1086/605546pmid: N/A
We have used the Spitzer Space Telescope InfraRed Spectrograph (IRS) 22-μm peakup array to observe thermal emission from the nucleus and trail of comet 103P/Hartley 2, the target of NASA’s Deep Impact Extended Investigation (DIXI). The comet was observed on UT 2008 August 12 and 13, while 5.5 AU from the Sun. We obtained two 200 frame sets of photometric imaging over a 2.7 hr period. To within the errors of the measurement, we find no detection of any temporal variation between the two images. The comet showed extended emission beyond a point source in the form of a faint trail directed along the comet’s antivelocity vector. After modeling and removing the trail emission, a NEATM model for the nuclear emission with beaming parameter of 0.95 ± 0.20 indicates a small effective radius for the nucleus of 0.57 ± 0.08 km and low geometric albedo 0.028 ± 0.009 (1σ). With this nucleus size and a water production rate of 3 × 1028 molecules s-1 at perihelion, we estimate that ∼100% of the surface area is actively emitting volatile material at perihelion. Reports of emission activity out to ∼5 AU support our finding of a highly active nuclear surface. Compared to Deep Impact’s first target, comet 9P/Tempel 1, Hartley 2’s nucleus is one-fifth as wide (and about one-hundredth the mass) while producing a similar amount of outgassing at perihelion with about 13 times the active surface fraction. Unlike Tempel 1, comet Hartley 2 should be highly susceptible to jet driven spin-up torques, and so could be rotating at a much higher frequency. Since the amplitude of nongravitational forces are surprisingly similar for both comets, close to the ensemble average for ecliptic comets, we conclude that comet Hartley 2 must have a much more isotropic pattern of time-averaged outgassing from its nuclear surface. Barring a catastrophic breakup or major fragmentation event, the comet should be able to survive up to another 100 apparitions (∼700 yr) at its current rate of mass loss.
Where Is the Best Site on Earth? Domes A, B, C, and F, and Ridges A and BSaunders, Will; Lawrence, Jon S.; Storey, John W. V.; Ashley, Michael C. B.; Kato, Seiji; Minnis, Patrick; Winker, David M.; Liu, Guiping; Kulesa, Craig
doi: 10.1086/605780pmid: N/A
The Antarctic plateau contains the best sites on earth for many forms of astronomy, but none of the existing bases was selected with astronomy as the primary motivation. In this article, we try to systematically compare the merits of potential observatory sites. We include South Pole, Domes A, C, and F, and also Ridge B (running northeast from Dome A), and what we call “Ridge A” (running southwest from Dome A). Our analysis combines satellite data, published results, and atmospheric models, to compare the boundary layer, weather, aurorae, airglow, precipitable water vapor, thermal sky emission, surface temperature, and the free atmosphere, at each site. We find that all Antarctic sites are likely to be compromised for optical work by airglow and aurorae. Of the sites with existing bases, Dome A is easily the best overall; but we find that Ridge A offers an even better site. We also find that Dome F is a remarkably good site. Dome C is less good as a thermal infrared or terahertz site, but would be able to take advantage of a predicted “OH hole” over Antarctica during spring.
Stellar Spectropolarimetry with Retarder Waveplate and Beam Splitter DevicesBagnulo, S.; Landolfi, M.; Landstreet, J. D.; Landi Degl’Innocenti, E.; Fossati, L.; Sterzik, M.
doi: 10.1086/605654pmid: N/A
Nighttime polarimetric measurements are often obtained very close to the limits of the instrumental capabilities. It is important to be aware of the possible sources of spurious polarization, and to adopt data reduction techniques that best compensate for the instrumental effects intrinsic to the design of the most common polarimeters adopted for nighttime observations. We define a self-consistent framework starting from the basic definitions of the Stokes parameters, and we present an analytical description of the data reduction techniques commonly used with a polarimeter (consisting of a retarder wave plate and a Wollaston prism) to explore their advantages and limitations. We first consider an ideal polarimeter in which all optical components are perfectly defined by their nominal characteristics. We then introduce deviations from the nominal behavior of the polarimetric optics, and develop an analytical model to describe the polarization of the outgoing radiation. We study and compare the results of two different data reduction methods, one based on the differences of the signals, and one based on their ratios, to evaluate the residual amount of spurious polarization. We show that data reduction techniques may fully compensate for small deviations of the polarimetric optics from their nominal values, although some important (first-order) corrections have to be adopted for linear polarization data. We include a detailed discussion of quality checking by means of null parameters. We present an application to data obtained with the FORS1 instrument of the ESO VLT, in which we have detected a significant amount of cross talk between circular and linear polarization. We show that this cross-talk effect is not due to the polarimetric optics themselves, but is most likely caused by spurious birefringence due to the instrument’s collimator lens.
Systemic: A Testbed for Characterizing the Detection of Extrasolar Planets. I. The Systemic Console PackageMeschiari, Stefano; Wolf, Aaron S.; Rivera, Eugenio; Laughlin, Gregory; Vogt, Steve; Butler, Paul
doi: 10.1086/605730pmid: N/A
We present the Systemic Console, a new all-in-one, general-purpose software package for the analysis and combined multiparameter fitting of Doppler radial velocity (RV) and transit timing observations. We give an overview of the computational algorithms implemented in the console, and describe the tools offered for streamlining the characterization of planetary systems. We illustrate the capabilities of the package by analyzing an updated radial velocity data set for the HD 128311 planetary system. HD 128311 harbors a pair of planets that appear to be participating in a 2:1 mean motion resonance. We show that the dynamical configuration cannot be fully determined from the current data. We find that if a planetary system like HD 128311 is found to undergo transits, then self-consistent Newtonian fits to combined radial velocity data and a small number of timing measurements of transit midpoints can provide an immediate and vastly improved characterization of the planet’s dynamical state.
The Minimum Mass Ratio for Contact Close Binary Systems of W Ursae Majoris-typeArbutina, Bojan
doi: 10.1086/605616pmid: N/A
Extreme mass ratio close binaries of W UMa-type represent an interesting class of objects in which ∼1M⊙ main-sequence star is in contact with a significantly less massive companion (M2 ∼ 0.1M⊙). Earlier theoretical investigations of these systems found that there is a minimum mass ratio q = M2/M1 ≈ 0.085 - 0.095 (obtained for n = 3 polytrope–fully radiative primary) above which these systems are stable. If the mass ratio is lower than minimum, a tidal instability develops (Darwin’s instability). This instability, which is secular, growing on a viscous dissipation timescale, eventually forces the stars to merge into a single, rapidly rotating object (such as FK Com-type stars or blue stragglers), implying that such systems would not be observed. There appear to be, however, some W UMa-type binaries with empirically obtained q values below the theoretical limit for stability. The aim of this dissertation was to try to resolve the discrepancy between theory and observations by considering rotating polytropes. Other candidate systems for stellar mergers such as AM CVn-type stars have also been discussed in the dissertation.