Engineering topics

Panagia, N.

Publications and source records attributed to Panagia, N..

At least 19 records

NASA NTRS2013

Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. I. Observational Overview and First Results

The Hubble Tarantula Treasury Project (HTTP) is an ongoing panchromatic imaging survey of stellar populations in the Tarantula Nebula in the Large Magellanic Cloud that reaches into the sub-solar mass regime (<0.5 Stellar Mass). HTTP utilizes the capability of the Hubble Space Telescope to operate the Advanced Camera for Surveys and the Wide Field Camera 3 in parallel to study this remarkable region in the near-ultraviolet, optical, and near-infrared spectral regions, including narrow-band H(alpha) images. The combination of all these bands provides a unique multi-band view. The resulting maps of the stellar content of the Tarantula Nebula within its main body provide the basis for investigations of star formation in an environment resembling the extreme conditions found in starburst galaxies and in the early universe. Access to detailed properties of individual stars allows us to begin to reconstruct the temporal and spatial evolution of the stellar skeleton of the Tarantula Nebula over space and time on a sub-parsec scale. In this first paper we describe the observing strategy, the photometric techniques, and the upcoming data products from this survey and present preliminary results obtained from the analysis of the initial set of near-infrared observations.

Tarantula↗

NASA NTRS2011

X-Ray Illumination of the Ejecta of Supernova 1987A

When a massive star explodes as a supernova, substantial amounts of radioactive elements-primarily Ni-56, Ni-57 and Ti-44 are produced. After the initial from shock heating, the light emitted by the supernova is due to the decay of these elements. However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium. The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellan Cloud. From 1994 to 200l, the ejecta faded owing to radioactive decay of Ti-44 as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejects, enabling us to analyse the structure and chemistry of the vanished star.

Larsson, J.↗

NASA NTRS2007

The UDF05 Follow-up of the HUDF: I. The Faint-End Slope of the Lyman-Break Galaxy Population at zeta approx. 5

We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP, and NICMOS (Fll0W, Fl60W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z approximately 5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V - i, i - z selection criterion, we identify a sample of 101 and 133 candidate z approximately 5 galaxies down to z(sub 850) = 28.5 and 29.25 magnitudes in the NICP12 field and in the HUDF, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 Angstroms LBG LF over the range M(sub 1400) = [-22.2, -17.1], i.e. down to approximately 0.04 L(sub *) at z = 5. We show that: (i) Different assumptions for the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z = 5 (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z = 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha approximately -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z = 3 and z = 6. Our study therefore supports no variation in the faint-end of the LBG LF over the whole redshift range z = 3 to z = 6. The comparison with theoretical predictions suggests that (a,) the majority of the stars in the z = 5 LBG population are produced with a Top-Heavy IMF in merger-driven starbursts, and that (b) possibly, either the fraction of stellar mass produced in starburst, or the fraction of high mass stars in the bursts is increased towards the bright end of the LF.

Oesch, P. A.↗

NASA NTRS2000

Supernovae at the Highest Angular Resolution

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supernovae radio astronomy VLBI X-Ray astronomy Hu↗

NASA NTRS2000

Supernovae at the Highest Angular Resolution

The study of supernovae (SNe) and their environments in host galaxies at the highest possible angular resolution in a number of wavelength regimes is providing vital clues to the nature of their progenitor stars.

supernovae raido astronomy VLBI X-ray Astronomy Ga↗

NASA NTRS2000

Supernovae at the Highest Angular Resolution

Telescope↗

NASA NTRS1999

Cepheid Calibration of the Peak Brightness of SNe Ia.: SN 1989B in NGC 3627 - 9

Repeated imaging observations have been made of NGC 3627 with the Hubble Space Telescope in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F8141,V band. The galaxy hosted the prototypical, "Branch normal", type la supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 days to 3.85 days. The de-reddened distance modulus is determined to be (m - M)(sub 0) = 30.22 +/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. The photometric data of Wells et al. (1994), combined with the Cepheid data for NGC 3627 give MB(max) = -19.36 +/- 0.18 and M(sub V)(max) = -19.34 +/- 0.16 for SN 1989B. Combined with the previous six calibrations in this program, plus two additional calibrations determined by others gives the mean absolute magnitudes at maximum of (M(sub B)) = -19.48 +/- 0.07 for "Brunch normal" SNe Ia at this interim stage in the calibration program. Using the argument by Wells et al. (1994) that SN 1989B here is virtually identical in decay rate and colors at maximum with SN 198ON in NGC 1316 in the Fornax cluster, and that such identity means nearly identical absolute magnitude, it follows that the difference in the distance modulus of NGC 3627 and NGC 1316 is 1.62 +/- 0.03 mag. Thus the NGC 3627 modulus implies that (m - M)(sub 0) = 31.84 for NGC 1316. The second parameter correlations of M(max) of blue SNe la with decay rate, color at maximum, and Hubble type are re-investigated. The dependence of (M(max)) on decay rate is non-linear, showing a minimum for decay rates between 1.0 less than ADelta(sub m)15 less than 1.6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe la with decay-rate data and the current eight calibrating SNe la for the correlation with decay rate as well as color gives H(sub 0) = 60 +/- 2 (internal) km/s Mpc, in both B and V. The same value to within 4% is obtained if only the SNe la in spirals (without second parameter corrections) are considered. The correlation of SNe la color at maximum with M(max) cannot be due to internal absorption because the slope coefficients in B, V, and I with the change in magnitude are far from or even opposite to the canonical reddening values. The color effect must be intrinsic to the supernova physics. "Absorption" corrections of distant blue SNe la will lead to incorrect values of H(sub 0). The Cepheid distances used in this series are insensitive to metallicity differences. The zeropoint of the P-L relation is based on an assumed LMC modulus of (m - M)(sub 0) = 18.50. As this may have to be increased by 0(sup m).06 to 0(sup m).08, all distances in this paper will follow and Ho will decrease by 3 - 4%.

Saha, A.↗

NASA NTRS1995

Discovery of Cepheids in NGC 5253: Absolute peak brightness of SN Ia 1895B and SN Ia 1972E and the value of H(sub 0)

Observations of the Hubble Space Telescope (HST) between 1993 May 31 and 1993 July 19 in 20 epochs in the F555W passband and five epochs in the F785LP passband have led to the discovery of 14 Cepheids in the Amorphous galaxy NGC 5253. The apparent V distance modulus is (m-M)(sub AV) = 28.08 +/- 0.10 determined from the 12 Cepheids with normal amplitudes. The distance modulus using the F785LP data is consistent with the V value to within the errors. Five methods used to determine the internal reddening are consistent with zero differential reddening, accurate to a level of E(B-V) less than 0.05 mag, over the region occupied by Cepheids and the two supernovae (SNe) produced by NGC 5253. The apparent magnitudes at maximum for the two SNe in NGC 5253 are adopted as B(sub max) = 8.33 +/- 0.2 mag for SN 1895B, and B(sub max) = 8.56 +/- 0.1 and V(sub max) = 8.60 +/- 0.1 for SN 1972E which is a prototype SN of Type Ia. The apparent magnitude system used by Walker (1923) for SN 1859B has been corrected to the modern B scale and zero point to determine its adopted B(sub max) value.

Saha, A.↗

NASA NTRS1994

WFPC2 observations of the double cluster NGC 1850 in the Large Magellanic Cloud

Hubble Space Telescope-Wide Field/Planetary Camera-2 (HST-WFPC2) optical and ultraviolet imaging observations of the young double cluster NGC 1850 in the Large Magellanic Cloud (LMC) are presented. The main cluster, NGC 1850A, is a globular-like cluster and has an age of 50 +/- 10 Myr, while the subcluster, NGC 1850B, which is more loosely distributed, is very young at 4.3 +/- 0.9 Myr. Its young age is confirmed by the detection of a pre-main-sequence population of stars associated to it. The two clusters have considerably different IMF slopes, with the main cluster having a flat slope (f(m) proportional to m(exp -1.4 +/- 0.2)) and the young cluster a much steeper one (f(m) proportional to m(exp -2.6 +/- -0.1)). The LMC field star population displays a broad range of ages, from approximately 0.5 Gyr up to more than 4 Gyr.

Gilmozzi, R.↗

NASA NTRS1994

Observations of SN 1987A with the COSTAR-corrected Faint Object Camera

New near-ultraviolet and visible (O III) observations of SN 1987A obtained 2511 and 2533 days after outburst with the Corrective Optics Space Telescope Axial Replacement (COSTAR) corrected Faint Object Camera (FOC) on board the Hubble Space Telescope (HST) are presented. Even though the supernova is now very faint (m approximately equal to 19), the new data are of dramatically higher quality than those obtained previously with the aberrated telescope. The images -- which are now no longer hampered by the spherical aberration halos of the two nearby companion stars -- reveal a well-resolved symmetrical expanding envelope that can be traced out to a radius of approximately equal to 275 mas or approximately equal to 9400 km/s in the near-UV. The apparent diameter of the ejecta has grown to 255 +/- 2 mas Full Width at Half Maximum (FWHM) in the near-UV and 167 +/- 5 mas (FWHM) in the visible, in close agreement with the expansion rates inferred from earlier FOC observations obtained on days 1275 and 1754. The improved shell-like crescent has started to form within the inner approximately equals 60 mas core of the nebula.

Jakobsen, P.↗

NASA NTRS1993

An atlas of ultraviolet spectra of star-forming galaxies

A systematic study is presented of the UV spectra of star-forming galaxies of different morphological type and activity class using a sample drawn from a uniformly reduced IUE data set. The spectra for a wide variety of galaxies, including normal spiral, LINER, starburst, blue compact, blue compact dwarf, and Seyfert 2 galaxies, are presented in the form of spectral energy distributions to demonstrate the overall characteristics according to morphology and activity class and in the form of absolute flux distributions to better show the absorption and emission features of individual objects. The data support the picture based on UV spectra of the Orbiting Astronomical Observatory and of the Astronautical Netherlands Satellite that spiral galaxies of later Hubble class have more flux at the shortest UV wavelengths than do spiral galaxies of earlier Hubble class.

Kinney, A. L.↗

NASA NTRS1993

Faint object camera observations of the shape and expansion of SN 1987A

A comparison is made between HST Faint-Object Camera visible and near-IR imagery of SN 1987A obtained 1754 days after outburst and those obtained after 1278 days. The SN has dimmed by a factor of 0.35 +/- 0.04 between the two observations; this corresponds to an exponential decay time 450 +/- 50 days. Detailed fits to image profiles show that this SN's envelope is heavily limb-darkened, and well-characterized by a surface brightness profile that decreases with angular radius. The apparent size of the envelope also varies significantly with wavelength.

Jakobsen, P.↗

NASA NTRS1993

Everything you ever wanted to know about the ultraviolet spectra of star-forming galaxies but were afraid to ask

We present ultraviolet spectra of 143 star-forming galaxies of different morphological types and activity classes including S0, Sa, Sb, Sc, Sd, irregular, starburst, blue compact, blue compact dwarf, Liner, and Seyfert 2 galaxies. These IUE spectra cover the wavelength range from 1200 to 3200 A and are taken in a large aperture (10 x 20 inch). The ultraviolet spectral energy distributions are shown for a subset of the galaxies, ordered by spectral index, and separated by type for normal galaxies, Liners, starburst galaxies, blue compact (BCG) and blue compact dwarf (BCDG) galaxies, and Seyfert 2 galaxies. The ultraviolet spectra of Liners are, for the most part, indistinguishable from the spectra of normal galaxies. Starburst galaxies have a large range of ultraviolet slope, from blue to red. The star-forming galaxies which are the bluest in the optical (BCG and BCDG), also have the 'bluest' average ultraviolet slope of beta = -1.75 +/- 0.63. Seyfert 2 galaxies are the only galaxies in the sample that consistently have detectable UV emission lines.

Kinney, A. L.↗

NASA NTRS1993

Ultraviolet spectroscopy of Nova Muscae 1991

We report on a series of ultraviolet spectroscopic observations made with the IUE satellite, which sampled critical outburst stages of the soft X-ray transient Nova Muscae 1991. Continuum light curves, and a multi-epoch line analysis are presented. In addition, a single epoch optical-UV spectra obtained with the HST/FOS is discussed. The optical-UV continuum fits approximately the 'canonical' fv varies as V exp 1/3 power low expected for thermal emission from steady state accretion disk. The emission line spectrum contains prominent high ionization lines of C IV and N V. Weaker lines are seen at intermittent epochs, including some of lower ionization. The derivation of galactic reddening which has significant implications for distance estimates is discussed. Comparisons with previous SXT sources are considered.

Shrader, C. R.↗

NASA NTRS1992

The Hubble Space Telescope observations of X-ray nova Muscae 1991 and its spectral evolution

Hubble Space Telescope Faint Object Spectrograph (FOS) Faint Object Camera (FOC) and observations of Nova Muscae 1991 obtained on May 14-15, 1991 are presented and discussed. A nearly featureless continuum with broad 2200 A absorption feature and no Balmer jump is found. The FOS spectrum is modeled, including previous multiepoch IUE, optical, and X-ray data using a simple blackbody accretion disk model. It is found that the mass transfer rate decays exponentially with a characteristic time of about 43 days. The cooling front predicted by the disk instability model should have been observable, but was not seen.

Cheng, F. H.↗

NASA NTRS1991

Properties of the SN 1987A circumstellar ring and the distance to the Large Magellanic Cloud

The distance to SN 1987A was determined by comparing the angular size of its circumstellar ring, measured from an HST image obtained in a narrow forbidden O III 5007 A filter, with its absolute size derived from an analysis of the light curves of narrow UV lines measured with the IUE. The analysis confirms that the observed elliptical structure is a circular ring seen at a mean inclination of i = 42.8 + or - 2.6 deg and provides a determination of its absolute diameter of (1.27 + or - 0.07) x 10 to the 18th cm. Its ratio to the angular diameter of 1.66 + or - 0.03 arcsec gives an accurate determination of the distance to SN 1987A, i.e., d(1987A) = 51.2 + or - 3.1 kpc.

Panagia, N.↗

NASA NTRS1989

Narrow ultraviolet emission lines from SN 1987A - Evidence for CNO processing in the progenitor

Results from UV observations of SN 1987A with the IUE satellite are presented, showing that emission lines of He II, C III, N III, N IV, N V, and O III increase in strength with time after May 24, 1987. It is found that increased emission originated in a photoionized low-density circumstellar gas, lost by the progenitor in its red supergiant phase. A nebular analysis reveals a large nitrogen overabundance, indicating that the gas has undergone substantial CNO processing. This suggests that the progenitor of SN 1987A lost much of its hydrogen envelope before the explosion. The findings are consistent with models in which a red supergiant evolves to the blue supergiant stage before exploding.

Fransson, C.↗

NASA NTRS1983

X-ray and ultraviolet observations of extragalactic H II regions

The dwarf galaxies NGC 5204, NGC 5474, and NGC 5585 have been shown by Sandage and Tammann (1974) to be physically associated with M101 (distance 7.2 Mpc). The present investigation is concerned with observations of the dwarf galaxies in the M101 group conducted with the aid of the Einstein satellite. Upon detection of X-ray emission from NGC 5204, it was found possible to observe this galaxy also with the International Ultraviolet Explorer (IUE). It is now feasible to compare the predictions on the stellar population of the galaxy inferred from the X-ray data with a more direct measure concerning this population. It is found that the hypothesis regarding the responsibility of binary X-ray sources of Population I progenitors for most of the X-ray emission is strengthened by the IUE short-wavelength spectrum of NGC 5204.

Fabbiano, G.↗