We present the optical transmission spectrum of the highly inflated Saturn- mass exoplanet WASP-21b, using three transits obtained with the ACAM instrument on the William Herschel Telescope through the LRG-BEASTS survey (Low Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy). Our transmission spectrum covers a wavelength range of 4635-9000{AA}, achieving an average transit depth precision of 197ppm compared to one atmospheric scale height at 246ppm. We detect NaI absorption in a bin width of 30{AA}, at >4{sigma} confidence, which extends over 100{AA}. We see no evidence of absorption from KI. Atmospheric retrieval analysis of the scattering slope indicates it is too steep for Rayleigh scattering from H_2, but is very similar to that of HD 189733b. The features observed in our transmission spectrum cannot be caused by stellar activity alone, with photometric monitoring of WASP-21 showing it to be an inactive star. We therefore conclude that aerosols in the atmosphere of WASP-21b are giving rise to the steep slope that we observe, and that WASP-21b is an excellent target for infra-red observations to constrain its atmospheric metallicity.
We used the Gran Telescopio Canarias (GTC) instrument OSIRIS to obtain long-slit spectra in the optical range 520-1040nm of the planetary host star WASP-43 and of a reference star during a full primary transit event. We integrated the stellar flux of both stars in different wavelength regions producing several light curves. We measure a mean planet-to-star radius ratio in the white light curve of 0.15988^+0.00133^_-0.00145_. We present a tentative detection in the planet-to-star radius ratio around the NaI doublet ({lambda} 588.9, 589.5nm) when compared to the nearby continuum at the 2.9-sigma level. We find no significant excess of the measured planet-to-star radius ratio around the KI doublet ({lambda} 766.5nm, 769.9nm) when compared to the nearby continuum.
We present Herschel/HIFI observations of 14 water lines in a small sample of galactic massive protostellar objects: NGC6334I(N), DR21(OH), IRAS16272-4837, and IRAS05358+3543. Using water as a tracer of the structure and kinematics, we aim to individually study each of these objects, to estimate the amount of water around them, but to also shed light on the high-mass star formation process. We analyze the gas dynamics from the line profiles using Herschel-HIFI observations acquired as part of the WISH key-project of 14 far-IR water lines (water, H_2_^17^O, H_2_^18^O), and several other species. Then through modeling of the observations using the RATRAN radiative transfer code, we estimate outflow, infall, turbulent velocities, molecular abundances, and investigate any correlation with the evolutionary status of each source. The four sources (plus previously studied W43-MM1) have been ordered in terms of evolution based on their SED: NGC64334I(N)-W43-MM1-DR21(OH)-IRAS16272-4837-IRAS05358+3543. The molecular line profiles exhibit a broad component coming from the shocks along the cavity walls associated with the protostars, and an infalling (or expansion for IRAS05358+3543) and passively heated envelope component, with highly supersonic turbulence likely increasing with the distance from the center. Accretion rates between 6.3x10^-5^ and 5.6x10^-4^M_{sun}_/yr are derived from the infall observed in three of our sources. The outer water abundance is estimated to be at the typical value of a few 10^-8^ while the inner abundance varies from 1.7x10^-6^ to 1.4x10^-4^ with respect to H_2_ depending on the source. We confirm that regions of massive star formation are highly turbulent and that the turbulence likely increases in the envelope with the distance to the star. The inner abundances are lower than the expected 10^-4^ perhaps because our observed lines do not probe deep enough into the inner envelope, or because photodissociation through protostellar UV photons is more efficient than expected. We show that the higher the infall/expansion velocity in the protostellar envelope, the higher is the inner abundance, maybe indicating that larger infall/expansion velocities generate shocks that will sputter water from the ice mantles of dust grains in the inner region. High-velocity water must be formed in the gas-phase from shocked material.
Thorium-Argon lamps are commonly used as wavelength calibration units at moderately high spectral resolutions because of the richness of the thorium spectrum in the visual. The inclusion of blended lines whose position is assumed to coincide with the laboratory wavelength of the main component is shown to result in a calibration precision significantly worse than the intrinsic random noise limit. In order to avoid this degradation of the calibration, we present resolution-dependent Th-Ar wavelengths in the region 277 to >1000nm for use at pixel-scales (pixel-size expressed in wavelength units) between {lambda}/2.5x10+4 and {lambda}/10+5.
A collection of data for 115 extinction curves derived from low-dispersion IUE spectra are presented with normalization to E(B-V)=1. The electronic Atlas of Extinctions contains the list of the stars used, their association membership, and the normalized extinctions for 88 wavelength values between 1260 and 3000 Angstroems.
With only a few low- and high-mass star-formation regions studied in detail so far, it is unclear what role the environment plays in complex molecule formation. In this light, a comparison of relative abundances of related species between sources might be useful for explaining any observed differences. We seek to measure the relative abundance between three important complex organic molecules, ethylene glycol ((CH_2_OH)_2_), glycolaldehyde (CH_2_OHCHO) and methyl formate (HCOOCH_3_), toward high-mass protostars and thereby provide additional constraints on their formation pathways. We use IRAM30 m single-dish observations of the three species toward two high-mass star-forming regions - W51/e2 and G34.3+0.2 - and report a tentative detection of (CH_2_OH)_2_ toward both sources.
The ionizing continuum from active galactic nuclei is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes on to supermassive black holes. Using Hubble Space Telescope's Wide Field Camera 3, we have constructed the first stacked ultraviolet (rest-frame wavelengths 600-2500{AA}) spectrum of 53 luminous quasars at z=~2.4, with a state-of-the-art correction for the intervening Lyman forest and Lyman continuum absorption. The continuum slope (f_{nu}_{prop.to}{nu}^{alpha}{nu}^) of the full sample shows a break at ~912{AA} with spectral index {alpha}_{nu}_=-0.61+/-0.01 at {lambda}>912{AA} and a softening at shorter wavelengths ({alpha}_{nu}_=-1.70+/-0.61 at {lambda}<=912{AA}). Our analysis proves that a proper intergalactic medium absorption correction is required to establish the intrinsic continuum emission of quasars. We interpret our average ultraviolet spectrum in the context of photoionization, accretion disc models, and quasar contribution to the ultraviolet background. We find that observed broad line ratios are consistent with those predicted assuming an ionizing slope of {alpha}_ion_=-2.0, similar to the observed ionizing spectrum in the same wavelength range. The continuum break and softening are consistent with accretion disc plus X-ray corona models when black hole spin is taken into account. Our spectral energy distribution yields a 30 per cent increase to previous estimates of the specific quasar emissivity, such that quasars may contribute significantly to the total specific Lyman limit emissivity estimated from the Ly{alpha} forest at z<3.2.
We present a method which uses cuts in colour-colour and reduced proper motion-colour space to select white dwarfs without the recourse to spectroscopy while allowing an adjustable compromise between completeness and efficiency. Rather than just producing a list of white dwarf candidates, our method calculates a probability of being a white dwarf (P_WD_) for any object with available multiband photometry and proper motion. We applied this method to all objects in the Sloan Digital Sky Survey (SDSS) Data Release 10 (DR10) photometric footprint and to a few selected sources in DR7 which did not have reliable photometry in DR9 or DR10. This application results in a sample of 61 969 DR10 and 3799 DR7 photometric sources with calculated P_WD_ from which it is possible to select a sample of ~23000 high-fidelity white dwarf candidates with T_eff_>~7000K and g<=19. This sample contains over 14000 high confidence white dwarfs candidates which have not yet received spectroscopic follow-up. These numbers show that, to date, the spectroscopic coverage of white dwarfs in the SDSS photometric footprint is, on average, only ~40 percent complete. While we describe here in detail the application of our selection to the SDSS catalogue, the same method could easily be applied to other multicolour, large area surveys. We also publish a list of 8701 bright (g<=19) white dwarfs with SDSS spectroscopy, of which 1781 are new identifications in DR9/DR10.
White dwarfs (WDs) are excellent forensic tools for studying end-of-life issues surrounding low- and intermediate-mass stars, and the old, solar metallicity open star cluster Messier 67 is a proven laboratory for the study of stellar evolution for solar-type stars. In this paper, we present a detailed spectroscopic study of brighter (M_g_<=12.4) WDs in Messier 67, and in combination with previously published proper motion membership determinations, we identify a clean, representative sample of cluster WDs, including 13 members with hydrogen-dominated atmospheres, at least one of which is a candidate double degenerate, and 5 members with helium-dominated atmospheres. Using this sample we test multiple predictions surrounding the final stages of stellar evolution in solar-type stars. In particular, the stochasticity of the integrated mass lost by ~1.5 solar mass stars is less than 7% of the WD remnant mass. We identify WDs likely resulting from binary evolution, including at least one blue straggler remnant and two helium-core WDs. We observe no evidence of a significant population of helium-core WDs formed by enhanced mass loss on the red giant branch of the cluster. The distribution of WD atmospheric compositions is fully consistent with that in the field, limiting proposed mechanisms for the suppression of helium atmosphere WD formation in star clusters. In short, the WD population of Messier 67 is fully consistent with basic predictions of single- and multiple-star stellar evolution theories for solar metallicity stars.
We present a spectroscopic analysis of white dwarfs found in the Kiso survey. Spectroscopic observations at high signal-to-noise ratio have been obtained for all DA and DB stars in the Kiso Schmidt ultraviolet excess survey (KUV stars). These observations led to the reclassification of several KUV objects, including the discovery of three unresolved DA+DB double-degenerate binaries. The atmospheric parameters (T_eff_ and logg) are obtained from detailed model atmosphere fits to optical spectroscopic data. The mass distribution of our sample is characterized by a mean value of 0.606M_{sun}_ and a dispersion of 0.135M_{sun}_ for DA stars, and 0.758M_{sun}_ and a dispersion of 0.192M_{sun}_ for DB stars. Absolute visual magnitudes obtained from our spectroscopic fits allow us to derive an improved luminosity function for the DA and DB stars identified in the Kiso survey. Our luminosity function is found to be significantly different from earlier estimates based on empirical photometric calibrations of M_V_ for the same sample. The results for the DA stars now appear entirely consistent with those obtained for the PG survey using the same spectroscopic approach. The space density for DA stars with M_V_<=12.75 is 2.80x10^-4^pc^-3^ in the Kiso survey, which is 9.6% smaller than the value found in the PG survey.
