Perry Greenfield

Astropy: A community Python package for astronomy

We present the first public version (v0.2) of the open-source and community-developed Python package, Astropy. This package provides core astronomy-related functionality to the community, including support for domain-specific file formats such as flexible image transport system (FITS) files, Virtual Observatory (VO) tables, and common ASCII table formats, unit and physical quantity conversions, physical constants specific to astronomy, celestial coordinate and time transformations, world coordinate system (WCS) support, generalized containers for representing gridded as well as tabular data, and a framework for cosmological transformations and conversions. Significant functionality is under active development, such as a model fitting framework, VO client and server tools, and aperture and point spread function (PSF) photometry tools. The core development team is actively making additions and enhancements to the current code base, and we encourage anyone interested to participate in the development of future Astropy versions.

Mapping AG Carinae : long-split spectroscopy and coronographic imaging of the nebula and jet

New high-resolution images of the nebula around the luminous blue variable AG Carinae have been obtained with the Johns Hopkins Adaptive Optics Coronograph at the Swope 40 inch (1 m) telescope, Las Campanas, in the light of Hα + [N II] and in a narrow V continuum. The images confirm the presence of highly axisymmetric features in AG Carinaes circumstellar environment. In addition, new, high signal-to-noise ratio long-slit spectroscopic data are presented, in the spectral range (6363-7254 A), spatial resolution 0.89 ″/pixel, and spectral resolution 40 km/s, with full spatial coverage of the nebula

Discovery of an optical synchrotron jet in 3C 264

We report the discovery of a new optical synchrotron jet in the radio galaxy 3C 15. This brings to nine the number of known optical synchrotron jets in nearby radio galaxies. The jet is well resolved in both length and width and extends to a projected metric distance of ~5 kpc from the galaxy nucleus. The host galaxy shows complex inner structure, including a dust lane and what appears to be two, or possibly three, emission filaments or arms. On average the optical jet is bluer than the host galaxy by about 0.4 mag. Unlike other galaxies hosting optical jets, the core of the galaxy does not possess a bright, unresolved nucleus, suggesting that the active galactic nucleus is presently inactive or buried in dust. The radio-optical spectral index, αro ~ 1, is the softest yet observed for radio galaxies with optical jets. The observed disturbances in the nuclear regions are indicative of a recent merger or infall possibly resulting in the ejection of material along the jet.

Preliminary analysis of an ultraviolet Hubble Space Telescope faint object camera image of the center of M31

A 5161 s exposure was taken with the FOC on the central 44 arcsec of M31, through a filter centered at 1750 A. Much of the light is redleak from visible wavelengths, but nearly half of it is genuine UV. The image shows the same central peak found earlier by Stratoscope, with a somewhat steeper dropoff outside that peak. More than 100 individual objects are seen, some pointlike and some slightly extended. We identify them as post-asymptotic giant branch stars, some of them surrounded by a contribution from their accompanying planetary nebulae. These objects contribute almost a fifth of the total UV light, but fall far short of accounting for all of it. We suggest that the remainder may result from the corresponding evolutionary tracks in a population more metal-rich than solar.

Learning from FITS: Limitations in use in modern astronomical research

The Flexible Image Transport System (FITS) standard has been a great boon to astronomy, allowing observatories, scientists and the public to exchange astronomical information easily. The FITS standard, however, is showing its age. Developed in the late 1970s, the FITS authors made a number of implementation choices that, while common at the time, are now seen to limit its utility with modern data. The authors of the FITS standard could not anticipate the challenges which we are facing today in astronomical computing. Difficulties we now face include, but are not limited to, addressing the need to handle an expanded range of specialized data product types (data models), being more conducive to the networked exchange and storage of data, handling very large datasets, and capturing significantly more complex metadata and data relationships. There are members of the community today who find some or all of these limitations unworkable, and have decided to move ahead with storing data in other formats. If this fragmentation continues, we risk abandoning the advantages of broad interoperability, and ready archivability, that the FITS format provides for astronomy. In this paper we detail some selected important problems which exist within the FITS standard today. These problems may provide insight into deeper underlying issues which reside in the format and we provide a discussion of some lessons learned. It is not our intention here to prescribe specific remedies to these issues; rather, it is to call attention of the FITS and greater astronomical computing communities to these problems in the hope that it will spur action to address them.

High-resolution imaging of the Pluto-Charon system with the Faint Object Camera of the Hubble Space Telescope

Images of the Pluto-Charon system were obtained with the Faint Object Camera (FOC) of the Hubble Space Telescope (HST) after the refurbishment of the telescope. The images are of superb quality, allowing the determination of radii, fluxes, and albedos. Attempts were made to improve the resolution of the already diffraction limited images by image restoration. These yielded indications of surface albedo distributions qualitatively consistent with models derived from observations of Pluto-Charon mutual eclipses.

Reaching for the Stars with Python

The author describes how Python has helped scientists calibrate and analyze data from the Hubble Space Telescope, first as a means of scripting legacy applications, and, more recently, as a way of developing new applications in Python itself.

First results from the Faint Object Camera : high-resolution observations of the central object R136 in the 30 Doradus nebula

R136 is the luminous central object of the giant H II region 30 Doradus in the Large Magellanic Cloud. We report on the first high-resolution observations of R136 with the Faint Object Camera on board the Hubble Space Telescope. The physical nature of the brightest component R136a has been a matter of some controversy over the last few years. The UV images obtained show that R131a is a very compact star cluster consisting of more than eight stars within 0″.7 diameter. From these high-resolution images a mass upper limit can be derived for the most luminous stars observed in R136

Faint Object Camera far-ultraviolet objective prism observations of 12 z>3 quasars

We present the first results of an exploratory objective prism survey of the far-ultraviolet (λλ1200-1800) spectra of high-redshift quasars obtained with the Faint Object Camera on-board the Hubble Space Telescope. The prime objective of this survey is to identify one or more candidates among the known quasars at z em >3 with sufficient flux at far-ultraviolet wavelengths to enable detailed follow-up observations of redshifted intergalactic He II λ304 absorption using the HST grating spectrographs. FOC prism observations of 12 prime candidates selected for redshift (z em ≃3.03-3.66), brightness (V≤18.5) and the appearance of their optical absorption spectra are presented and discussed

First results from the faint object camera - High-resolution imaging of the Pluto-Charon system

The first observations of a solar system target with the Faint Object Camera of the HST are reported. Observations of the Pluto-Charon system were obtained in f/96 and f/288 mode. Pluto and Charon were clearly resolved, and the observed separation and diameters are in accordance with expectations. The f/96 data were astrometrically and photometrically analyzed; preliminary results are presented.