Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

Young galaxy candidates in the hubble frontier fields. iii. macs. j0717.5+3745

Abstract: In this paper we present the results of our search for and study of z ≳ 6 galaxy candidates behind the third Frontier Fields (FFs) cluster, MACS J0717.5+3745, and its parallel field, combining data from Hubble and Spitzer. We select 39 candidates using the Lyman break technique, for which the clear non-detection in optical make the extreme mid-z interlopers hypothesis unlikely. We also take benefit from z ≳ 6 samples selected using the previous FF data sets of Abell 2744 and MACS 0416 to improve the constraints on the properties of very high redshift objects. We compute the redshift and the physical properties such emission lines properties, star formation rate, reddening, and stellar mass for all FF objects from their spectral energy distribution using templates including nebular emission lines. We study the relationship between several physical properties and confirm the trend already observed in previous surveys for evolution of star formation rate with galaxy mass and between the size and the UV luminosity of our candidates. The analysis of the evolution of the UV luminosity function with redshift seems more compatible with an evolution of density. Moreover, no robust z ⩾ 8.5 object is selected behind the cluster field and few z ~ 9 candidates have been selected in the two previous data sets from this legacy survey, suggesting a strong evolution in the number density of galaxies between z ~ 8 and 9. Thanks to the use of the lensing cluster, we study the evolution of the star formation rate density produced by galaxies with L > 0.03 L^*, and confirm the strong decrease observed between z ~ 8 and 9.

Adaptive optics infrared imaging polarimetry and optical hst imaging of hubble's variable nebula (R monocerotis/NGC 2261): A close look at a very young active herbig Ae/Be star

Abstract: We present high-resolution (FWHM = 02) near-IR (J, H, and K') adaptive optics images of the Herbig Ae/Be star R Monocerotis Optical Hubble Space Telescope (HST) WFPC2 PC camera archival images are also presented For the first time, adaptive optics was utilized to make high-resolution (FWHM = 02) IR-imaging polarimetry maps of R Mon In addition, the first mid-IR array images (at 117 and 208 ?m) of R Mon have been obtained We also present new 316, 393, and 467 ?m images We have found that R Mon is a 069 binary star with a companion that dereddens onto the classical T Tauri locus Based on the near-infrared photometry of this companion we believe it is a 15 M?, very young ( + 800?280 pc distant based on previous proper-motion and radial velocity measurements of R Mon's jet Our high-resolution (FWHM ~ 02) adaptive optics infrared polarimetry maps agree with the current interpretation that NGC 2261 is a reflection nebula illuminated by R Mon Interior to the parabolic shell there is a complex of twisted filaments along the eastern edge These filaments resemble a double-helical structure which is well described by a power law from ~103 to 105 AU from R Mon This double helix may trace a twisted magnetic field above R Mon Based on H I emission-line ratios, we find the direct extinction toward R Mon to be AV = 131 mag in the infrared (? > 128 ?m), falling to a lower value of AV = 36 mag in the optical (? < 128 ?m), where scattered light increasingly lowers the effective extinction in the line ratios The large AV = 131 extinction is likely due to the dusty atmosphere of an inclined R ~ 100 AU optically thick accretion disk surrounding R Mon A simple model of such an accretion disk + star system (with Macc ~ 8 ? 10-5 M? yr-1, M* = 104 M?, R* = 2 R?, and T* ~ 35 ? 104 K) reproduces the observed dereddened R Mon spectral energy distribution (SED) from the optical (04 ?m) to the millimeter region Consideration of the lower extinction (AV = 36) on the path followed by the scattered visible light eliminated any need for an inner gap in the accretion disk model to reproduce the SED In general, young stellar objects (YSOs) that are obscured in the optical but directly visible in the infrared will have different effective optical and infrared extinctions Infrared extinctions derived from optical observations dominated by scattered light will be underestimates of the true IR extinction along the direct path The use of an independent estimator of both the optical and infrared extinctions such as common upper-level H I recombination lines is highly desirable The utilization of the correct optical and infrared extinctions may relieve the need for optically thin inner-disk gaps to explain YSO near-IR SEDs

Testing EUV/X-Ray Atomic Data for the Solar Dynamics Observatory

Abstract: The Atmospheric Imaging Assembly (AIA) and the Extreme-ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) include spectral windows in the X-ray/EUV band. Accuracy and completeness of the atomic data in this wavelength range is essential for interpretation of the spectrum and irradiance of the solar corona, and of SDO observations made with the AIA and EVE instruments. Here, we test the X-ray/EUV data in the CHIANTI database to assess their completeness and accuracy in the SDO bands, with particular focus on the 94 A and 131 A AIA passbands. Given the paucity of solar observations adequate for this purpose, we use high-resolution X-ray spectra of the low-activity solar-like corona of Procyon obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We find that while spectral models overall can reproduce quite well the observed spectra in the soft X-ray range {lambda} {approx} 130 A, they significantly underestimate the observed flux in the 50-130 A wavelength range. The model underestimates the observed flux by a variable factor ranging from Almost-Equal-To 1.5, at short wavelengths below {approx}50 A, up to Almost-Equal-To 5-7 in the {approx}70-125 A range. In the AIAmore » bands covered by LETGS, i.e., 94 A and 131 A, we find that the observed flux can be underestimated by large factors ({approx}3 and {approx}1.9, respectively, for the case of Procyon presented here). We discuss the consequences for analysis of AIA data and possible empirical corrections to the AIA responses to model more realistically the coronal emission in these passbands.« less

Found: the progenitors of AM CVn and supernovae .Ia

Abstract: We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141.18−014120.9 (J0751) is an eclipsing double WD binary containing a 0.19 M⊙ WD with a 0.97 M⊙ companion in a 1.9 h orbit. J0751 becomes the fifth eclipsing double WD system currently known. SDSS J174140.49+652638.7 (J1741) is another binary containing a 0.17 M⊙ WD with an unseen M ≥ 1.11 M⊙ WD companion in a 1.5-h orbit. With a mass ratio of ≈0.1, J1741 will have stable mass transfer through an accretion disc and turn into an interacting AM Canum Venaticorum (AM CVn) system in the next ≈160 Myr. With a mass ratio of 0.2, J0751 is likely to follow a similar evolutionary path. These are the first known AM CVn progenitor binary systems and they provide important constraints on the initial conditions for AM CVn. Theoretical studies suggest that both J0751 and J1741 may create thermonuclear supernovae in ∼108 yr, either .Ia or Ia. Such explosions can account for ∼1 per cent of the Type Ia supernova rate.

Results of a Deep Imaging Survey of One Square Degree of the Pleiades for Low-Luminosity Cluster Members

Abstract: We have obtained relatively deep imaging in two colors, with limiting magnitudes of V ~ 22.5 and Ic ~ 21, of about one square degree of the Pleiades open cluster. Our primary goal was to identify new candidate brown dwarf members of this ~100 Myr-old open cluster. In the process, we have also obtained V and Ic photometry for a large number of brighter proper-motion members of the cluster for which only photographic photometry had been available up until now. We identify six candidate objects whose locations in a V versus (V - I)c color-magnitude diagram are consistent with their being Pleiades members near or below the hydrogen-burning mass limit. We have obtained near-infrared photometry for several of these brown dwarf candidates, as well as for a selection of previously identified very low mass Pleiades members, and we use this new photometry to help determine whether the objects identified in the visual are indeed Pleiades members or not. Finally, we have obtained a moderate-resolution spectrum of one of the new brown dwarf candidates with the Keck LRIS spectrograph. The spectrum shows that the star has a spectral type of M7, which is compatible with its photometric colors, and that it has an Hα equivalent width of about 14 A and a marginally detected lithium 6708 A absorption equivalent width of about 0.4 A. These spectroscopic characteristics suggest that this object (MHObd1) is indeed a Pleiades member with a mass at or slightly above the hydrogen-burning mass limit.