Strengthening the Case for Asteroidal Accrection: Evidence for Subtle and Diverse Disks at White Dwarfs

Spitzer Space Telescope IRAC 3-8 micron and AKARI IRC 2-4 micron photometry are reported for ten white dwarfs with photospheric heavy elements; nine relatively cool stars with photospheric calcium, and one hotter star with a peculiar high carbon abundance. A substantial infrared excess is detected at HE 2221-1630, while modest excess emissions are identified at HE 0106-3253 and HE 0307+0746, implying these latter two stars have relatively narrow (Delta r < 0.1 Rsol) rings of circumstellar dust. A likely 7.9 micron excess is found at PG 1225-079 and may represent, together with G166-58, a sub-class of dust ring with a large inner hole. The existence of attenuated disks at white dwarfs substantiates the connection between their photospheric heavy elements and the accretion of disrupted minor planets, indicating many polluted white dwarfs may harbor orbiting dust, even those lacking an obvious infrared excess.Comment: 13 pages, emulateapj, accepted to Ap

The Luminosity and Mass Functions of Low-Mass Stars in the Galactic Disk: I. The Calibration Region

We present measurements of the luminosity and mass functions of low-mass stars constructed from a catalog of matched Sloan Digital Sky Survey (SDSS) and 2 Micron All Sky Survey (2MASS) detections. This photometric catalog contains more than 25,000 matched SDSS and 2MASS point sources spanning ~30 square degrees on the sky. We have obtained follow-up spectroscopy, complete to J=16, of more than 500 low mass dwarf candidates within a 1 square degree sub-sample, and thousands of additional dwarf candidates in the remaining 29 square degrees. This spectroscopic sample verifies that the photometric sample is complete, uncontaminated, and unbiased at the 99% level globally, and at the 95% level in each color range. We use this sample to derive the luminosity and mass functions of low-mass stars over nearly a decade in mass (0.7 M_sun > M_* > 0.1 M_sun). We find that the logarithmically binned mass function is best fit with an M_c=0.29 log-normal distribution, with a 90% confidence interval of M_c=0.20--0.50. These 90% confidence intervals correspond to linearly binned mass functions peaking between 0.27 M_sun and 0.12 M_sun, where the best fit MF turns over at 0.17 M_sun. A power law fit to the entire mass range sampled here, however, returns a best fit of alpha=1.1 (where the Salpeter slope is alpha = 2.35). These results agree well with most previous investigations, though differences in the analytic formalisms adopted to describe those mass functions can give the false impression of disagreement. Given the richness of modern-day astronomical datasets, we are entering the regime whereby stronger conclusions can be drawn by comparing the actual datapoints measured in different mass functions, rather than the results of analytic analyses that impose structure on the data a priori. (abridged)Comment: Accepted for publication in the Astronomical Journal. 21 pages, emulateapj format, 12 figures. Figures 1, 4, 11 and 12 degraded for astroph; full resolution version available for download at http://www.cfa.harvard.edu/~kcovey

New instruments for second servicing mission.

"May 1995"--Cover."Available in cycle 7; do not propose for in cycle 6"--Cover."This document describes observing capabilities that are to be offered on H[ubble] S[pace] T[elescope] in the next call for proposals"--P. 1.Cover title.Near infrared camera and multi-object spectrometer instrument mini-handbook -- Space telescope imaging spectrograph instrument mini-handbook.Mode of access: Internet

M83 volume densities of giant molecular clouds

VizieR online Data Catalogue associated with article published in journal Astronomy &amp; Astrophysics with title 'The volume densities of giant molecular clouds in M83.' (bibcode: 2008A&amp;A...489..533H

Episodic accretion in magnetically layered protoplanetary discs

We study protoplanetary disc evolution assuming that angular momentum transport is driven by gravitational instability at large radii, and magnetohydrodynamic (MHD) turbulence in the hot inner regions. At radii of the order of 1 AU such discs develop a magnetically layered structure, with accretion occurring in an ionized surface layer overlying quiescent gas that is too cool to sustain MHD turbulence. We show that layered discs are subject to a limit cycle instability, in which accretion onto the protostar occurs in #propor to#10&quot;4 yr bursts with M#propor to#10&quot;-&quot;5M_sunyr&quot;-&quot;1, separated by quiescent intervals lasting #propor to#10&quot;5 yr where M#approx#10&quot;-&quot;8M_sunyr&quot;-&quot;1. Such bursts could lead to repeated episodes of strong mass outflow in Young Stellar Objects. The transition to this episodic mode of accretion occurs at an early epoch (t&lt;&lt;1 Myr), and the model therefore predicts that many young pre-main-sequence stars should have low rates of accretion through the inner disc. At ages of a few Myr, the discs are up to an order of magnitude more massive than the minimum mass solar nebula, with most of the mass locked up in the quiescent layer of the disc at r#propor to#1 AU. The predicted rate of low mass planetary migration is reduced at the outer edge of the layered disc, which could lead to an enhanced probability of giant planet formation at radii of 1-3 AU. (orig.)SIGLEAvailable from: http://www.mpa-garching.mpg.de / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Radio Sources in Low-Luminosity AGNs. IV

VizieR online Data Catalogue associated with article published in journal Astronomy &amp; Astrophysics with title 'Radio Sources in Low-Luminosity Active Galactic Nuclei. IV. Radio Luminosity Function, Importance of Jet Power, and Radio Properties of the Complete Palomar Sample' (bibcode: 2005A&amp;A...435..521N

Angular-momentum plane for disc galaxies

VizieR online Data Catalogue associated with article published in journal Astronomy &amp; Astrophysics with title 'A tight angular-momentum plane for disc galaxies.' (bibcode: 2021A&amp;A...651L..15M

Astronify: v0.1

Astronify contains tools for sonifying astronomical data. Currently Astronify can sonify data series. This package is under active development, and will ultimately grow to encompass a range of sonification functionality