Bryan Penprase | Pomona College (original) (raw)

Papers by Bryan Penprase

Bulletin of the American Astronomical Society, Oct 1, 2010

The Warm Spitzer NEO survey, ExploreNEOs, will observe approximately 700 Near Earth Asteroids. Se... more The Warm Spitzer NEO survey, ExploreNEOs, will observe approximately 700 Near Earth Asteroids. Several of these objects are known to be binary asteroid systems. Binary systems are interesting due to the unique opportunity they present for determining the masses and densities of their constituent bodies. The calculations rely on a variety of data sources. The geometric albedo and effective diameter

A Warm Spitzer survey of approximately 700 near-Earth objects (NEOs) has been started to derive a... more A Warm Spitzer survey of approximately 700 near-Earth objects (NEOs) has been started to derive albedos and diameters of the numerous small bodies. We present a ground-based NEO observation program designed to complement the Spitzer data. By using a variety of observational techniques, we aim to obtain optical magnitudes, lightcurves and compositional information for many of these objects. We have begun a program to obtain high-quality optical magnitudes of all 700 Spitzer targets, using a variety of telescope facilities with a range of apertures (from 0.36 m to 8 m). For a subset of our targets, we will also obtain lightcurves, which will be used as a proxy for the larger sample. We plan to obtain spectra of 250 objects from the Spitzer NEO sample and broadband spectrophotometric measurements of another 100. These spectroscopic results will allow us to derive compositions for nearly half our sample and act as a ground-truth for the larger, complete sample. Observations are already scheduled on the NASA Infrared Telescope Facility (SpeX as well as MIRSI, which will be used to confirm our Spitzer thermal observations and modeling), NOAO SMARTS telescopes, the Las Campanas 1-meter and several smaller telescopes. We will continue to expand the range of facilities used, matching aperture with target brightness. This catalog of objects will serve as a reference sample for a wide variety of future NEO studies.

The Astronomical Journal, Aug 9, 2010

We have begun the ExploreNEOs project in which we observe some 700 Near-Earth Objects (NEOs) at 3... more We have begun the ExploreNEOs project in which we observe some 700 Near-Earth Objects (NEOs) at 3.6 and 4.5 μm with the Spitzer Space Telescope in its Warm Spitzer mode. From these measurements and catalog optical photometry we derive albedos and diameters of the observed targets. The overall goal of our ExploreNEOs program is to study the history of near-Earth space by deriving the physical properties of a large number of NEOs. In this paper, we describe both the scientific and technical construction of our ExploreNEOs program. We present our observational, photometric, and thermal modeling techniques. We present results from the first 101 targets observed in this program. We find that the distribution of albedos in this first sample is quite broad, probably indicating a wide range of compositions within the NEO population. Many objects smaller than 1 km have high albedos (0.35), but few objects larger than 1 km have high albedos. This result is consistent with the idea that these larger objects are collisionally older, and therefore possess surfaces that are more space weathered and therefore darker, or are not subject to other surface rejuvenating events as frequently as smaller NEOs.

The Astronomical Journal, Feb 1, 2011

The Astronomical Journal, Aug 12, 2011

Examining the albedo distribution of the near-Earth object (NEO) population allows for a better u... more Examining the albedo distribution of the near-Earth object (NEO) population allows for a better understanding of the relationship between absolute (H) magnitude and size, which impacts calculations of the size frequency distribution and impact hazards. Examining NEO albedos also sheds light on the differences between the NEO and Main Belt populations. We combine albedo results from the ExploreNEOs Warm Spitzer Exploration Science program with taxonomic classifications from the literature, publicly available data sets, and new observations from our concurrent spectral survey to derive the average albedos for C-, D-, Q-, S-, V-, and X-complex NEOs. Using a sample size of 118 NEOs, we calculate average albedos of 0.29 +0.05 −0.04 , 0.26 +0.04 −0.03 , and 0.42 +0.13 −0.11 for the Q-, Sand nd V-complexes, respectively. The averages for the C-and D-complexes are 0.13 +0.06 −0.05 and 0.02 +0.02 −0.01 , but these averages are based on a small number of objects (five and two, respectively) and will improve with additional observations. We use albedos to assign X-complex asteroids to one of the E-, M-, or P-types. Our results demonstrate that the average albedos for the C-, S-, V-, and X-complexes are higher for NEOs than the corresponding averages observed in the Main Belt.

$Research paper thumbnail of Keck ESI Observations of Metal-Poor Damped Lyman-{\alpha} Systems$

arXiv (Cornell University), Jun 21, 2010

We present the first results from a survey of SDSS quasars selected for strong H I damped Lyman-α... more We present the first results from a survey of SDSS quasars selected for strong H I damped Lyman-α (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g. C II λ1334 and Si II λ1260). These metal-poor DLA candidates were selected from the SDSS DR5 quasar spectroscopic database, and comprise a large new sample for probing low metallicity galaxies. Medium-resolution echellette spectra from the Keck ESI spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleosynthetic patterns at these metallicities. We have estimated saturation corrections for the moderately under-resolved spectra, and systems with very narrow Doppler parameter (b ≤ 5 km s −1) will likely have underestimated abundances. For those systems with Doppler parameters b > 5 km s −1 , we have measured low metallicity DLA gas with [X/H] <-2.4 for at least one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that several DLA systems have [X/H] < −2.8, including five DLA systems with both low equivalent widths and low metallicity in transitions of both C II and O I. All of the measured DLA metallicities, however, exceed or are consistent with a metallicity of at least 1/1000 of solar, regardless of the effects of saturation in our spectra. Our results indicate that the 1 Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

We present our new polarimeter system which includes a combination of filter wheel, polarimeter a... more We present our new polarimeter system which includes a combination of filter wheel, polarimeter and spectrograph in one instrument. This instrument, funded by JPL and Pomona College, will be our primary optical instrument at the Pomona College 1-meter telescope in Wrightwood and combines several functions in one instrument. We present preliminary results, details of the design and user interface, which allows sequences of observations to be taken.

During the past several years, remote and robotic telescopes have enabled huge increases in obser... more During the past several years, remote and robotic telescopes have enabled huge increases in observing capabiltiies. We present the application of these technologies in undergraduate education at Pomona College. Our network of two 14" remotely operable telescopes, and a smaller 10" telescope enables us to perform remote observing during laboratory sessions. In addition we can remotely operate our 1-meter telescope at Wrightwood, and a variety of student and class research projects are possible with this network of telescopes. We present the research projects, and curriculum developed so far, and its role in undergraduate astronomy education.

We present the results of a remotely operated telescope known as PINTO, the Pomona College Intern... more We present the results of a remotely operated telescope known as PINTO, the Pomona College Internet Telescope, and the campaign for monitoring a sample of Near Earth Asteroids. We have observed over 150 asteroids with the system, and we present some of the details of the Python-based robotic control system, and our data reduction pipeline. Our PINTO telescope is based in New Mexico, but is controlled by a set of Python routines that generate NEO ephemeris data, schedule and execute observations, and automatically sequence the observations with standard star observations. In addition, we have enabled our Claremont, CA telescopes for remote operation, and we describe some of our plans for using the network of telescope for asteroid study and transient followup.

Proceedings of the International Astronomical Union, 2011

Type Ia supernovae are very good tools for measuring distances on a cosmic scale. The consensus v... more Type Ia supernovae are very good tools for measuring distances on a cosmic scale. The consensus view is that mass transfer onto a white dwarf in a close binary system leads to a thermonuclear explosion, though the nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star. In the double-degenerate model it is another white dwarf. We study the velocity structure of absorbing material along the line of sight to 35 Type Ia supernovae and find a statistical preference for blueshifted structures, likely arising in gas outflows from the supernova progenitor systems, consistent with a single-degenerate progenitor for a substantial fraction of Type Ia supernovae in nearby spiral galaxies.

We present new results from a campaign to detect interstellar absorption from High Velocity Cloud... more We present new results from a campaign to detect interstellar absorption from High Velocity Cloud and Cirrus sightlines near quasars with detected absorption. The new observations provide limits on the distances to the cirrus and HVC complex, and in some cases the detected CaII, NaI and other species provide constraints on the kinematics, column densities, and physical state of the

Images of the main belt asteroid 42 Isis were taken on March 1, 4, 6, 9, and 11 of 2008 with the ... more Images of the main belt asteroid 42 Isis were taken on March 1, 4, 6, 9, and 11 of 2008 with the 1-meter telescope at Table Mountain Observatory in SDSS g and r bands. These data were taken in conjunction with Spitzer Space Telescope observations of 42 Isis on March 6, 2008. Photometry was carried out on the images, and

We report new spectroscopic and photometric observations of the Draco Molecular Cloud, one of the... more We report new spectroscopic and photometric observations of the Draco Molecular Cloud, one of the most interesting and distant known high galactic latitude molecular clouds. We have detected photometric reddening and optical Na I D absorption lines from a large sample of stars, using telescopes at Palomar, and La Palma. By estimating the expected starcounts using a model of the galactic halo and comparing with our observed star counts we derive a photometric distance estimate of 1100 pc, with a best fit of 2.0 < Av < 3.0 magnitudes. The spectroscopic results allow us to estimate the distance to the cloud by using spectroscopic parallaxes for our sample of 15 stars with high dispersion spectra, and the spectroscopic distance is consistent with the photometric results, giving a distance of approximately 1000 pc. We also report some new results on other molecular clouds and high latitude features observed using high dispersion spectroscopy to reveal the distance and kinematics of...

The Astrophysical Journal, 2010

The Astrophysical Journal, 2013

The version presented here may differ from the published version or from the version of the recor... more The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription.

The Astronomical Journal, 2011

The Astronomical Journal, 2010

We have begun the ExploreNEOs project in which we observe some 700 Near Earth Objects (NEOs) at 3... more We have begun the ExploreNEOs project in which we observe some 700 Near Earth Objects (NEOs) at 3.6 and 4.5 microns with the Spitzer Space Telescope in its Warm Spitzer mode. From these measurements and catalog optical photometry we derive albedos and diameters of the observed targets. The overall goal of our ExploreNEOs program is to study the history of near-Earth space by deriving the physical properties of a large number of NEOs. In this paper we describe both the scientific and technical construction of our ExploreNEOs program. We present our observational, photometric, and thermal modeling techniques. We present results from the first 101 targets observed in this program. We find that the distribution of albedos in this first sample is quite broad, probably indicating a wide range of compositions within the NEO population. Many objects smaller than one kilometer have high albedos (0.35), but few objects larger than one kilometer have high albedos. This result is consistent with the idea that these larger objects are collisionally older, and therefore possess surfaces that are more space weathered and therefore darker, or are not subject to other surface rejuvenating events as frequently as smaller NEOs.