Space Telescope Science Institute Research Articles

Final Calibration of the WFPC2 Emission-Line Filters1,1Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA Contract No. NAS 5-26555.22Based on observations at the San Pedro Martir Observatory, operated by the Universidad Nacional Autónoma de México.

ABSTRACTFlux calibrated emission-line images can be obtained with the Hubble Space Telescope’s WFPC2 images through application of a series of steps. Corrections for the underlying continuum are necessary in some cases, as are corrections for nearby emission-lines that contaminate measurement of primary emission lines. However, the most important factor is usually the primary calibration coefficient, and this is best determined from in-orbit observations of extended nebula that have accurate ground-based flux calibrated observations. The secondary coefficients, which are only used to determine the small correction terms, can only be determined through use of the relative values of the camera characteristics determined prior to installation in orbit. Determination of the primary flux calibration coefficients have been made for WFPC2 filters using new observations of the Orion Nebula and the Ring Nebula. Primary and secondary calibration coefficients are given for the F469N, F487N, F502N, F656N, F658N, and F673N filters and their use in deriving flux-calibrated images from pipeline-processed images is described. There is no evidence for long-term variations in the calibration of these filters.

The Time History of Events and Macroscale Interactions during Substorms (THEMIS) Education and Outreach (E/PO) Program

During the pre-launch phase of NASA’s THEMIS mission, the Education and Public Outreach (E/PO) program successfully brought the excitement of THEMIS to the public, students and teachers through a variety of programs. The Geomagnetic Event Observation Network by Students (GEONS) was the main effort during this time, a project in which 13 magnetometers were placed in or near 13 rural schools across the country. High school teachers and a few middle school teachers at these and/or neighboring schools took part in a long-term professional development program based around space science and the magnetometer data. The teachers created week-long to semester-long projects during which their students worked on THEMIS lessons that they, their colleagues, and the E/PO team created. In addition to this program, THEMIS E/PO also launched the only Lawrence Hall of Science (LHS) Great Explorations in Mathematics and Science (GEMS) site in Nevada. This site provides a sustainable place for teacher professional development using hands-on GEMS activities, and has been used by teachers around the state of Nevada. Short-term professional development for K-12 teachers (one-hour to two-day workshops), with a focus on the Tribal College and Society for the Advancement of Chicanos and Native Americans in Science (SACNAS) communities have reached hundreds of teachers across the country. A Space Telescope Science Institute (STScI) ViewSpace show on auroras and THEMIS was created and distributed, and shown in over a hundred science centers and museums nationwide. The THEMIS E/PO program developed and maintained a THEMIS E/PO Website for dissemination of (1) information and multimedia about the science and engineering of THEMIS, (2) updated news about the mission in language appropriate for the public, (3) the GEONS data, the GEONS teacher guides with classroom activities, and (4) information about the THEMIS E/PO program. Hundreds of thousands of visitors have viewed this website. In this paper, we describe these programs along with the evaluation results, and discuss what lessons we learned along the way.

An Upper Mass Limit on a Red Supergiant Progenitor for the Type II-Plateau Supernova SN 2006my11Some 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 the National Aeronautics and Space Administration. The Observatory was made possible by the

ABSTRACTWe analyze two pre-supernova (SN) and three post-SN high-resolution images of the site of the Type II-Plateau supernova SN 2006my in an effort to either detect the progenitor star or to constrain its properties. Following image registration, we find that an isolated stellar object is not detected at the location of SN 2006my in either of the two pre-SN images. In the first, an I-band image obtained with the Wide-Field and Planetary Camera 2 on board the Hubble Space Telescope, the offset between the SN 2006my location and a detected source (“Source 1”) is too large: ≥0.08′′, which corresponds to a confidence level of non-association of 96% from our most liberal estimates of the transformation and measurement uncertainties. In the second, a similarly obtained V-band image, a source is detected (“Source 2”) that has overlap with the SN 2006my location but is definitively an extended object. Through artificial star tests carried out on the precise location of SN 2006my in the images, we derive a 3 σ upper bound on the luminosity of a red supergiant that could have remained undetected in our pre-SN images of log L/L⊙ = 5.10, which translates to an upper bound on such a star’s initial mass of 15 M⊙ from the STARS stellar evolutionary models. Although considered unlikely, we can not rule out the possibility that part of the light comprising Source 1, which exhibits a slight extension relative to other point sources in the image, or part of the light contributing to the extended Source 2, may be due to the progenitor of SN 2006my. Only additional, high-resolution observations of the site taken after SN 2006my has faded beyond detection can confirm or reject these possibilities.

The Hubble Legacy Archive NICMOS grism data

The Hubble Legacy Archive (HLA) aims to create calibrated science data from the Hubble Space Telescope archive and make them accessible via user-friendly and Virtual Observatory (VO) compatible interfaces. It is a collaboration between the Space Telescope Science Institute (STScI), the Canadian Astronomy Data Centre (CADC) and the Space Telescope - European Coordinating Facility (ST-ECF). Data produced by the Hubble Space Telescope (HST) instruments with slitless spectroscopy modes are among the most difficult to extract and exploit. As part of the HLA project, the ST-ECF aims to provide calibrated spectra for objects observed with these HST slitless modes. In this paper, we present the HLA NICMOS G141 grism spectra. We describe in detail the calibration, data reduction and spectrum extraction methods used to produce the extracted spectra. The quality of the extracted spectra and associated direct images is demonstrated through comparison with near-IR imaging catalogues and existing near-IR spectroscopy. The output data products and their associated metadata are publicly available through a web form at this http URL and via VO interfaces. In total, 2470 spectra of 1923 unique targets are included in the current release.

NGC 602 Environment, Kinematics and Origins1,1Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program number GO-10396. 22Based on observations obtained at the Anglo-Australian Telescope, Siding Spring, Australia.

ABSTRACTThe young star cluster NGC 602 and its associated HII region, N90, formed in a relatively isolated and diffuse environment in the Wing of the Small Magellanic Cloud. Its isolation from other regions of massive star formation and the relatively simple surrounding HI shell structure allows us to constrain the processes that may have led to its formation and to study conditions leading to massive star formation. We use images from the Hubble Space Telescope and high resolution echelle spectrographic data from the Anglo-Australian Telescope, along with 21 cm neutral hydrogen (HI) spectrum survey data and the shell catalog derived from it to establish a likely evolutionary scenario leading to the formation of NGC 602. We identify a distinct HI cloud component that is likely the progenitor cloud of the cluster and HII region, which probably formed in blister fashion from the cloud’s periphery. We also find that the past interaction of HI shells can explain the current location and radial velocity of the nebula. The surrounding interstellar medium is diffuse and dust-poor as demonstrated by a low visual optical depth throughout the nebula and an average HI density of the progenitor cloud estimated at 1 cm-3. These conditions suggest that the NGC 602 star formation event was produced by compression and turbulence associated with HI shell interactions. It therefore represents a single star-forming event in a low gas density region.

Understanding the 8 μm versus Paα Relationship on Subarcsecond Scales in Luminous Infrared Galaxies

14 pages, 9 figures, 4 tables.-- Based on observations obtained with T-ReCS instrument at the Gemini South Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: NSF (United States), PPARC (UK), NRC (Canada), CONICYT (Chile) ARC (Australia), CNPq (Brazil), and CONICET (Argentina).-- Also based on observations with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-266555.

Late-Time HST Photometry of SN 1994I: Hints of Positron Annihilation Energy Deposition11Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555. This research is primarily associated with proposal GO-5777.

ABSTRACTWe present multicolor Hubble Space Telescope (HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained ∼280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the γ-rays produced by the radioactive decay of 56Co diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.

A Hubble Space Telescope Survey of the Disk Cluster Population of M31. II. Advanced Camera for Surveys Pointings11Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for research in astronomy, Inc., under NASA contract NAS 5-26555.

ABSTRACTThis paper reports on a survey of star clusters in M31 based on archival images from the Hubble Space Telescope. Paper I reported results from images obtained with the Wide Field Planetary Camera 2 (WFPC2) and this paper reports results from the Advanced Camera for Surveys (ACS). The ACS survey has yielded a total of 339 star clusters, 52 of which—mostly globular clusters—were found to have been cataloged previously. As for the previous survey, the luminosity function of the clusters drops steeply for absolute magnitudes fainter than MV = -3; the implied cluster mass function has a turnover for masses less than a few hundred solar masses. The color-integrated magnitude diagram of clusters shows three significant features: (1) a group of very red, luminous objects: the globular clusters, (2) a wide range in color for the fainter clusters, representing a considerable range in age and reddening, and (3) a maximum density of clusters centered approximately at V = 21, B - V = 0.30, V - I = 0.50, where there are intermediate-age, intermediate-mass clusters with ages close to 500 million years and masses of about 2000 solar masses. We give a brief qualitative interpretation of the distribution of clusters in the CMDs in terms of their formation and destruction rates.

Dynamical Parameters for AM 0644−741

We present a simulation match to the 2004 Hubble Heritage high-resolution optical images of AM 0644-741. In N-body/smoothed particle hydrodynamics (SPH) simulations of AM 0644-741, we recreate the star formation features, as well as the underlying kinematics. Our simulations contain sufficient numerical density to accurately distinguish the overlapping/double ring, as well as the off-center nucleus seen in the radio observations of Higdon & Wallin and the young stellar features noted in the Space Telescope Science Institute Heritage observation. Derived star formation rates for the ring and nucleus match the observed star formation features, particularly when using a dρ/dt star formation formulation. Kinematic comparison with the results of Few and collaborators yields a match for the ring velocities but not necessarily the companion. We note that the gravity and gas dynamics, modeled by N-body plus SPH, dominate over feedback from stellar evolution effects (modeled using a variety of Schmidt-type parameters), resolving the dilemma posed by Cox and coworkers. Comparing our simulation to reality gives us insight into the ring longevity and likely generative impact scenario, reaffirming the collisional origins of this ring.

The GSC-II catalog release GSC 2.3: description and properties

AbstractThe GSC 2.3 is a current catalog release extracted from the Guide Star Catalog II database, which is maintained at the Space Telescope Science Institute in Baltimore, USA. The catalog contains astrometry, multi-band photometry (BJ,RJ,IN) and star/non-star classification for 945,592,683 objects down to the magnitude limit of the survey plates. We review the performance of stellar parameters, anticipating the improvements in astrometric accuracy foreseen by its recalibration with the newly available catalog in the UCAC series.

Dust and molecular content of the lensed quasar, MG0751+2716, atz = 3.2

Context: Gravitational lenses offer unique opportunities to explore the molecular content around active galactic nuclei at high redshift, through the magnification and gain in angular resolution. Aims: We study here the molecular and dust content of the high redshift (z=3.2), gravitationally lensed quasar MG0751+2716. Methods: We used the IRAM Plateau de Bure interferometer to measure the CO J=3-2, J=4-3 and J=8-7 rotation lines and continuum flux between 1.1 mm and 3 mm in MG0751+2716. We use HST data and constraints from the high resolution MERLIN map at 6.2 cm to build an improved model of the lens. Results: The position agreement between the CO emission and the millimeter continuum suggests that dust and molecules are closely related. A 500 km s-1 velocity gradient is tentatively detected from the CO lines across the central 0.5''. The continuum SED in the range 0.45 mm-204 mm exhibits the signatures of two components: synchrotron emission from a core/jet system, and thermal emission related to warm dust. The CO line intensities are compatible with warm, dense molecular gas, suggesting a location in the close environment of the quasar. These observational constraints lead us to consider a source/quasar model made of a point-like core, a radio jet, and a molecular and dusty ring-like structure (~460 pc in radius) located in a plane perpendicular to the jet axis and seen almost edge-on. For this configuration, we derive a total magnification of 16 for the quasar radiation at rest frequency above 350 GHz and a magnification of 25 below 350 GHz. The dust mass (assuming a likely temperature T=50 K) is M_dust=1.7 × 108 M_?, the mass of molecular material is M(H_2) = 6 × 1010 M_? and a lower limit to the dynamical mass is M_dyn = 1.5 × 1010 M_?. Such values are comparable to those found in the small sample of CO detected sources at high redshifts. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Based on observations obtained with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555.

Confirmation of New Planetary Nebulae in the Large Magellanic Cloud11Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5‐26555.

ABSTRACTWe present Hubble Space Telescope (HST) images of new planetary nebulae (PNe) that were discovered in the Reid‐Parker Anglo‐Australian Observatory/UK Schmidt Telescope Hα survey of the Large Magellanic Cloud. These serendipitous observations from various HST programs yield independent confirmations of six PNe; one other detected nebula may also be a PN, and one appears to be a region of diffuse emission. The high‐resolution HST archival images enable us to determine the physical sizes, nebular morphology, and related features of these new PNe in detail for the first time. In a few cases, we were also able to identify the central star, which was impossible with the lower resolution, wide‐field discovery data. The confirmation of faint, extended halos surrounding many PNe in the Reid‐Parker catalog must await the acquisition of new deep, high‐resolution, narrowband imagery.

A Hubble Space Telescope Survey of the Disk Cluster Population of M31. I. WFPC2 Pointings11Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5‐26555.

ABSTRACTAs a follow‐up to the automated cluster search carried out by Williams & Hodge, we have examined 39 Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) pointings to locate and study a comprehensive collection of disk clusters. The Williams technique was effective in finding young clusters, but not intermediate‐age or old clusters. Our searches have shown that M31 has large numbers of these intermediate and older open clusters, most of them undetected by both the Williams survey and other ground‐based searches. We present a catalog of 343 clusters detected on the WFPC2 images. Extrapolation from our data indicates that the entire disk of M31 contains approximately 80,000 star clusters. We have carried out integrated multicolor photometry of these clusters to ascertain their properties and to compare their properties with cluster systems of other galaxies. We show the cluster luminosity function, the color‐magnitude diagram, the formation function, and the size distribution. Cluster densities and colors show trends with disk position. An age distribution is derived and, although the ages are very uncertain for the fainter clusters, there is evidence for cluster dynamical destruction at about the same rate as in our Galaxy.

Cepheids in Multiple Systems: ADS 1485911Based on observations made with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5‐26555. These observations are associated with programs GO‐7478, GO‐8440, and GO‐8772.

ABSTRACTWe have attempted to resolve the system containing the Cepheid V1334 Cyg (=ADS 14859) using both the Faint Object Camera (FOC) and the Fine Guidance Sensor (FGS) on the Hubble Space Telescope, and also using ground‐based speckle interferometry with 4 m class instruments. None of these approaches was successful, leading to upper limits of approximately 20 mas (depending on the magnitude difference between the stars). We discuss constraints this places on a possible wide orbit as a guide to future observations.

Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations11Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5‐26555.

ABSTRACTA variety of on‐orbit imaging and spectroscopic observations are used to characterize the charge transfer efficiency (CTE) of the charge‐coupled device (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. A set of formulae is presented to correct observations of point sources for CTE‐related loss of signal. For data taken in imaging mode, the CTE loss is parameterized in terms of the location of the source on the CCD, the source signal level within the measurement aperture, the background level, and the time of observation. For spectroscopic data, it is found that one additional parameter is needed in order to provide an adequate calibration of the CTE loss, namely, the signal in the point‐spread function located between the signal extraction box and the readout amplifier. The effect of the latter parameter is significant for spectra taken using the G750L or G750M gratings of STIS. The algorithms presented here correct flux calibration inaccuracies due to CTE losses as large as 30% to within ∼1.5% rms throughout the wavelength range covered by the STIS CCD modes. This uncertainty is similar to the Poisson noise associated with a source detected at a signal level of about 2500 electrons per resolution element. Using bidirectional CCD readouts, centroid shifts incurred due to CTE loss are also derived. A tight correlation is found between the CTE loss and the centroid shift (both for imaging and for spectroscopic modes), thus enabling one to correct for both effects of imperfect charge transfer to STIS CCD observations.

Prototype development for a Hubble Legacy Archive

The Space Telescope Science Institute (STScI), in collaboration with the European Coordinating Facility (ECF), and the Canadian Astronomy Data Centre (CADC), is studying the development of an enhanced archive for the Hubble Space TelescopeHST), with the goal of improving the scientific value of the data. The primary enhancements would be:

Kinematics of the Narrow-Line Region in the Seyfert 2 Galaxy NGC 1068: Dynamical Effects of the Radio Jet

We present a study of high-resolution long-slit spectra of the narrow-line region (NLR) in NGC 1068 obtained with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope (HST). The spectra were retrieved from the Multimission Archive at the Space Telescope Science Institute obtained from two visits and seven orbits of HST time. We also obtained MERLIN radio maps of the center of NGC 1068 to examine the dependence of the NLR cloud velocities on the radio structure. The radial velocities and velocity dispersions of the bright NLR clouds appear to be unaffected by the radio knots, indicating that the radio jet is not the principal driving force on the outflowing NLR clouds. However, the velocities of the fainter NLR clouds are split near knots in the jet, indicating a possible interaction. Biconical outflow models were generated to match the data and for comparison to previous models done with lower dispersion observations. The general trend is an increase in radial velocity roughly proportional to distance from the nucleus followed by a linear decrease after roughly 100 pc similar to that seen in other Seyfert galaxies, indicating common acceleration and deceleration mechanisms.

Improvements to the Image Processing of Hubble Space Telescope NICMOS Observations with Multiple Readouts11Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5‐26555. These observations are associated with programs GO‐8088 and GO‐9075.

ABSTRACTWe report on improvements made to the standard NICMOS processing pipeline. The calculation of the uncertainties on the signal accumulation rate has been modified to include the statistical correlations between the consecutive readouts. This leads to a ∼30% correction in the photometric weight of individual pixels containing faint objects. In order to correct a problem with the existing cosmic‐ray rejection algorithm, we have developed and implemented a joint fit procedure, where the accumulating signal is fit as linear functions of time with the same rate both before and after the cosmic‐ray (CR) impact. This procedure leads to significantly smaller uncertainty in the count rate for pixels affected by CRs. We also show that regions neighboring CRs found by the standard NICMOS pipeline are systematically brighter. This interpixel correlation substantially increases the footprint of CR impacts and is treated for the first time by our new pipeline. The new processing is most relevant for photometry from deep observations of faint targets, for which accurate, optimal, and unbiased uncertainty estimates are important. We present examples of these improvements for deep NIC2 images of a high‐redshift supernova from the Supernova Cosmology Project. The net improvement is a factor of 2 reduction in the number of 3 σ photometric outliers.

EDUCATION: Touching the Void

It's like the ultimate adventure game: Board a spaceship, fly to a warped part of spacetime, and drop into a black hole. Welcome to the visually stunning Black Holes: Gravity's Relentless Pull. This month, astronomers Roeland van der Marel of the Space Telescope Science Institute in Baltimore, Maryland, and Gijs Verdoes Kleijn of the University of Groningen in the Netherlands received the €25,000 Pirelli INTERNETional Award for the educational Web site. Its encyclopedia offers background information on how black holes form, how long they last, and more. Chairborne astronauts can zip off to destinations such as Cygnus X-1, where a black hole is sucking matter from a nearby star. There, you can perform virtual experiments such as dropping a clock into the void: It ticks progressively slower and freezes on the edge of the black hole.

Variable Unidentified Emission near 6307 Å in η Carinae1,1This research is part of the Hubble Space Telescope Treasury Project for η Carinae, supported by grants GO‐9420 and GO‐9973 from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5‐26555. 22Partially based on observations obtained with UVES

ABSTRACTWe have discovered a conspicuous unidentified variable feature near 6307 Å in the spectrum of η Carinae that is spatially unresolved from the central star and its wind (r≲200–300 AU). It is significant for two reasons: first, such prominent unidentified lines are now rare in this object, and second, this feature varies strongly and systematically. It exhibits a combination of characteristics that, so far as we know, are unique in η Carinae’s spectrum. It may provide insights into the recurrent spectroscopic events and the star’s long‐term brightening.