49 research outputs found
Massive stars in massive clusters - IV. Disruption of clouds by momentum-driven winds
We examine the effect of momentum-driven OB-star stellar winds on a parameter space of simulated turbulent giant molecular clouds using smoothed particle hydrodynamic simulations. By comparison with identical simulations in which ionizing radiation was included instead of winds, we show that momentum-driven winds are considerably less effective in disrupting their host clouds than are H ii regions. The wind bubbles produced are smaller and generally smoother than the corresponding ionization-driven bubbles. Winds are roughly as effective in destroying the very dense gas in which the O stars are embedded, and thus shutting down the main regions of star-forming activity in the model clouds. However, their influence falls off rapidly with distance from the sources, so they are not as good at sweeping up dense gas and triggering star formation further out in the clouds. As a result, their effect on the star formation rate and efficiency is generally more negative than that of ionization, if they exert any effect at all.Peer reviewe
Ionisation-induced star formation III: Effects of external triggering on the IMF in clusters
We report on Smoothed Particle Hydrodynamics (SPH) simulations of the impact
on a turbulent M star--forming molecular cloud of
irradiation by an external source of ionizing photons. We find that the
ionizing radiation has a significant effect on the gas morphology, but a less
important role in triggering stars. The rate and morphology of star formation
are largely governed by the structure in the gas generated by the turbulent
velocity field, and feedback has no discernible effect on the stellar initial
mass function. Although many young stars are to be found in dense gas located
near an ionization front, most of these objects also form when feedback is
absent. Ionization has a stronger effect in diffuse regions of the cloud by
sweeping up low--density gas that would not otherwise form stars into
gravitationally--unstable clumps. However, even in these regions, dynamical
interactions between the stars rapidly erase the correlations between their
positions and velocities and that of the ionization front.Comment: 12 pages, 16 figures (some downgraded to fit on astro-ph), accepted
for publication in MNRA
Commissioning ShARCS: the Shane Adaptive optics infraRed Camera-Spectrograph for the Lick Observatory 3-m telescope
We describe the design and first-light early science performance of the Shane
Adaptive optics infraRed Camera-Spectrograph (ShARCS) on Lick Observatory's 3-m
Shane telescope. Designed to work with the new ShaneAO adaptive optics system,
ShARCS is capable of high-efficiency, diffraction-limited imaging and
low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a
HAWAII-2RG infrared detector, giving high quantum efficiency (>80%) and Nyquist
sampling the diffraction limit in all three wavelength bands. The ShARCS
instrument is also equipped for linear polarimetry and is sensitive down to 650
nm to support future visible-light adaptive optics capability. We report on the
early science data taken during commissioning.Comment: 9 pages, 7 figures. Presented at SPIE Astronomical Telescopes +
Instrumentation conference, paper 9148-11
Radiation Chemistry on Solar System Icy Bodies: Laboratory Simulations for Pluto and Other Transneptunian Objects
No abstract availabl
Supersonic Cloud Collision - I
It has long been suggested that shocks might play an important role in
altering the form of the interstellar medium (ISM). Shocks enhance gas density
and sufficiently dense regions may become self gravitating. Potential star
forming clouds within larger molecular clouds, move randomly at supersonic
speeds.
Depending on the precollision velocity, colliding molecular clouds produce a
slab that is either shock compressed or pressure confined. In a sequel of two
papers (I & II), we simulate molecular cloud collision and investigate the
dynamical evolution of such slabs. Shocked slabs are susceptible to
hydrodynamic instabilities and in the present paper (I) we study the effect of
strong shear between slab layers on the dynamic evolution of a shock compressed
gas slab. Both, head-on and off-centre cloud collisions have been examined in
this work. We include self gravity in all our simulations.
Simulations presented here, are performed using the smoothed particle
hydrodynamics (SPH) numerical scheme. Individual, pre-collision clouds are
modelled as pressure confined Bonnor-Ebert spheres. However, in the interest of
brevity the thermodynamic details of the problem are simplified and the gas
temperature is simply evolved by a barytropic equation of state. Obviously, the
gas, to some extent suffers from thermal inertial effects. However, we note
that the dynamical timescale is much smaller than the local sound crossing time
so that such effects should have minimum influence.Comment: 16 pages, 13 figures, 1 table; A&A accepted Typographical errors have
been attended to. The resolution of the figures has been deliberately lowered
in order to accommodate them all within the prescribed size limit
The modelling of feedback in star formation simulations
This document is the Accepted Manuscript version of the following article: James E. Dale, ‘The modelling of feedback in star formation simulations’, New Astronomy Reviews, Vol. 68, pp. 1-33, October 2015. This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. The final, published version is available online at doi:https://doi.org/10.1016/j.newar.2015.06.001. © 2015 Elsevier B.V. All rights reserved.I review the current state of numerical simulations of stellar feedback in the context of star formation at scales ranging from the formation of individual stars to models of galaxy formation including cosmic reionisation. I survey the wealth of algorithms developed recently to solve the radiative transfer problem and to simulate stellar winds, supernovae and protostellar jets. I discuss the results of these simulations with regard to star formation in molecular clouds, the interaction of different feedback mechanisms with each other and with magnetic fields, and in the wider context of galactic- and cosmological-scale simulations.Peer reviewe
Training of Instrumentalists and Development of New Technologies on SOFIA
This white paper is submitted to the Astronomy and Astrophysics 2010 Decadal
Survey (Astro2010)1 Committee on the State of the Profession to emphasize the
potential of the Stratospheric Observatory for Infrared Astronomy (SOFIA) to
contribute to the training of instrumentalists and observers, and to related
technology developments. This potential goes beyond the primary mission of
SOFIA, which is to carry out unique, high priority astronomical research.
SOFIA is a Boeing 747SP aircraft with a 2.5 meter telescope. It will enable
astronomical observations anywhere, any time, and at most wavelengths between
0.3 microns and 1.6 mm not accessible from ground-based observatories. These
attributes, accruing from the mobility and flight altitude of SOFIA, guarantee
a wealth of scientific return. Its instrument teams (nine in the first
generation) and guest investigators will do suborbital astronomy in a
shirt-sleeve environment. The project will invest $10M per year in science
instrument development over a lifetime of 20 years. This, frequent flight
opportunities, and operation that enables rapid changes of science instruments
and hands-on in-flight access to the instruments, assure a unique and extensive
potential - both for training young instrumentalists and for encouraging and
deploying nascent technologies. Novel instruments covering optical, infrared,
and submillimeter bands can be developed for and tested on SOFIA by their
developers (including apprentices) for their own observations and for those of
guest observers, to validate technologies and maximize observational
effectiveness.Comment: 10 pages, no figures, White Paper for Astro 2010 Survey Committee on
State of the Professio
The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey
We present the design and performance of the multi-object fiber spectrographs
for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon
Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999
on the 2.5-m aperture Sloan Telescope at Apache Point Observatory, the
spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II
surveys, enabling a wide variety of Galactic and extra-galactic science
including the first observation of baryon acoustic oscillations in 2005. The
spectrographs were upgraded in 2009 and are currently in use for BOSS, the
flagship survey of the third-generation SDSS-III project. BOSS will measure
redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyman-alpha
absorption of 160,000 high redshift quasars over 10,000 square degrees of sky,
making percent level measurements of the absolute cosmic distance scale of the
Universe and placing tight constraints on the equation of state of dark energy.
The twin multi-object fiber spectrographs utilize a simple optical layout
with reflective collimators, gratings, all-refractive cameras, and
state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in
two channels over a bandpass covering the near ultraviolet to the near
infrared, with a resolving power R = \lambda/FWHM ~ 2000. Building on proven
heritage, the spectrographs were upgraded for BOSS with volume-phase
holographic gratings and modern CCD detectors, improving the peak throughput by
nearly a factor of two, extending the bandpass to cover 360 < \lambda < 1000
nm, and increasing the number of fibers from 640 to 1000 per exposure. In this
paper we describe the original SDSS spectrograph design and the upgrades
implemented for BOSS, and document the predicted and measured performances.Comment: 43 pages, 42 figures, revised according to referee report and
accepted by AJ. Provides background for the instrument responsible for SDSS
and BOSS spectra. 4th in a series of survey technical papers released in
Summer 2012, including arXiv:1207.7137 (DR9), arXiv:1207.7326 (Spectral
Classification), and arXiv:1208.0022 (BOSS Overview