meena sahu - Academia.edu (original) (raw)

Papers by meena sahu

Astronomy and …, 1990

... regions where massive stars have been found (for the large range of determined [HCN]/[HNC] ra... more ... regions where massive stars have been found (for the large range of determined [HCN]/[HNC] ratios, ~-0.3...250, see eg Churchwell et al., 1984; Goldsmith et al ... Over the length of CG 1 the gradients reported by Schneps et al ... preprint Frerking, MA., Langer, WD, Wilson, RW : 1982 ...

We have assembled a unique, high signal-to-noise (S/N) spectrum of the hot metal-rich DA white dw... more We have assembled a unique, high signal-to-noise (S/N) spectrum of the hot metal-rich DA white dwarf, G191-B2B, from a coaddition of 22 E140H and 40 E230H STIS calibration spectra. This superb data set fully covers the wavelength range from 1155 A to 3169 A with S/N ranging from over 100 to 30; affording an unprecedentedly detailed view of the UV stellar absorption lines in a white dwarf star. We use this spectrum to search for a number of previously undiscovered heavy elements in the G191-B2B photosphere and to estimate elemental abundances and place upper limits on the abundances of a number of key species. An accurate photospheric inventory of heavy elements in hot degenerate stars is basic to our understanding of the chemical diffusion in these stars. These observations highlight the wealth of information present in echelle resolution spectra of white dwarfs such as G191-B2B and the need for a succeeding generation of UV instrumentation capable of providing data of this type for...

We have used the Big Throughput Camera at CTIO to image around the Hubble Deep Field--South in a ... more We have used the Big Throughput Camera at CTIO to image around the Hubble Deep Field--South in a narrow--band filter centered on Ly-alpha at the redshift of QSO J2233-606 (z=3D2.25). A total 4 hours of exposure reaches limits of 8.0*E(-17) ergs cm(-2) s(-1) (5sigma for point sources with 1.5arcsec seeing). The images cover 40\arcminx40' and sample a cube 60 co-moving

... However based on the recent ISSA maps and the study of the kinematics of the ionized gas in t... more ... However based on the recent ISSA maps and the study of the kinematics of the ionized gas in the region, we know that the IRAS Vela Shell and the Gum Nebula are two separate structures ... J. 206, 679 Weaver, R., McCray, CT, Castor, J., Shapiro, P., Moore, R.: 1977, Astrophys. ...

The ultraviolet spectrum (1145--1720A) of the distant quasar Q 0302--003 (z=3.286) was observed a... more The ultraviolet spectrum (1145--1720A) of the distant quasar Q 0302--003 (z=3.286) was observed at 1.8A resolution with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. A total integration time of 23,280 s was obtained. The spectrum clearly delineates the Gunn-Peterson HeII absorption trough, produced by HeII Lya, along the line of sight over the redshift range z=2.78-3.28. Its interpretation was facilitated by modeling based on Keck HIRES spectra of the HI Lya forest (provided by A. Songaila and by M. Rauch and W. Sargent). We find that near the quasar HeII Lya absorption is produced by discrete clouds, with no significant diffuse gas; this is attributed to a HeII "proximity effect" in which the quasar fully ionizes He in the diffuse intergalactic medium, but not the He in denser clouds. By two different methods we calculate that the average HeII Lya opacity at z 3.15 is tau >= 4.8. In the Dobrzycki-Bechtold void in the HI Lya forest near z=3...

We use ultraviolet spectra of Capella from the Hubble Space Telescope (HST) and Far Ultraviolet S... more We use ultraviolet spectra of Capella from the Hubble Space Telescope (HST) and Far Ultraviolet Spectroscopic Explorer (FUSE) satellites to study interstellar absorption lines from the Local Interstellar Cloud (LIC). Measurements of these lines are used to empirically determine the ionization states of carbon, nitrogen, and silicon in the LIC, for comparison with the predictions of theoretical photoionization models. We find that the observed ionization states are consistent with previously published photoionization predictions. Total abundances are determined for the elements mentioned above, and others, for comparison with solar abundances. Magnesium, aluminum, silicon, and iron are all depleted by at least a factor of 10 toward Capella. The abundances of carbon, nitrogen, and oxygen are essentially solar, although the error bars are large enough to also allow depletions of about a factor of 2 for these elements.

The ultraviolet spectrum (1145–1720 Å) of the distant quasar Q 0302–003 (z = 3.286) was observed ... more The ultraviolet spectrum (1145–1720 Å) of the distant quasar Q 0302–003 (z = 3.286) was observed at 1.8 Å resolution with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. A total integration time of 23,280 s was obtained. The spectrum clearly delineates the Gunn-Peterson He II absorption trough, produced by He II Lyα along the line of sight over the redshift range z = 2.78 − 3.28. Its interpretation was facilitated by modeling

The ultraviolet spectrum (1145–1720 Å) of the distant quasar Q 0302–003 (z = 3.286) was observed ... more The ultraviolet spectrum (1145–1720 Å) of the distant quasar Q 0302–003 (z = 3.286) was observed at 1.8 Å resolution during 10 orbits of the Hubble Space Telescope with the Space Telescope Imaging Spectrograph. A total integration time of 23,280 s was obtained. The spectrum clearly delineates the Gunn-Peterson He II absorption trough, produced by He II Lyα along the line of sight over the redshift range z = 2.78 − 3.28. Interpretation of the results was facilitated by modeling based on Keck HIRES spectra of the

AIP Conference Proceedings, 1997

The importance of studying absorption lines from z&Lt;0.1 galaxies are discussed. The Mg II λ... more The importance of studying absorption lines from z&Lt;0.1 galaxies are discussed. The Mg II λλ2796 and 2803 Å doublet absorption is sensitive to low column density gas and has been used to search for absorption lines from low-z galaxies. Recent studies of abundances and depletion patterns toward the Small Magellanic Cloud (Welty &etal; 1997) and the NGC 1705 sightline (Sahu & Blades, 1997) are reviewed.

Symposium - International Astronomical Union, 2000

Space Telescope Imaging Spectrograph (STIS) observations of the D/H ratio in the two velocity com... more Space Telescope Imaging Spectrograph (STIS) observations of the D/H ratio in the two velocity components towards G191-B2B are consistent with 1.5 ± 0.1 × 10−5 and do not agree with the values derived using the Goddard High Resolution Spectrograph (GHRS) data. We present some new work on the G191-B2B sightline, and the results we obtain are consistent with those of Sahu et al. (1999).

Astronomy and Astrophysics, Aug 30, 1994

Astronomy and Astrophysics, 1992

University of Groningen Thesis 1992, Aug 30, 1992

AIP Conference Proceedings, 1989

Primordial lithium abundance from interstellar lithium lines towards SN 1987A. [AIP Conference Pr... more Primordial lithium abundance from interstellar lithium lines towards SN 1987A. [AIP Conference Proceedings 183, 420 (1989)]. Kailash C. Sahu, SR Pottasch, Meenakshi Sahu. Abstract. The primoridal lithium abundance is known ...

Hst Proposal, Jul 1, 2000

Nato Asib Proc 105 White Dwarfs, 2003

We have obtained a very high quality spectrum of the white dwarf Sirius B with the Far Ultraviole... more We have obtained a very high quality spectrum of the white dwarf Sirius B with the Far Ultraviolet Spectroscopic Explorer (FUSE). The H I Lyman series from Ly beta through Ly 10 is evident, as are the quasi-molecular satellite features of Ly beta and Ly gamma. From this spectrum it will be possible to derive improved estimates of: 1) the gravitational redshift, 2) the surface gravity and 3) the photometric radius of the white dwarf. This should result in a substantial reduction of the current uncertainties in the spectroscopic mass and radius of Sirius B. We present preliminary results from these observations.

We present STIS--CCD spectra covering the range 2100-3100 Angstroms for both A&B images of the gr... more We present STIS--CCD spectra covering the range 2100-3100 Angstroms for both A&B images of the gravitational lens candidate UM 425. Although the spectrum of B has a low S/N ratio, we detect Broad Absorption Lines which confirms the lens nature of the system. We discuss the implications for the modelling of the lens.

Astronomy and …, 1990

The ultraviolet spectrum (1145–1720 Å) of the distant quasar Q 0302–003 (z = 3.286) was observed ... more The ultraviolet spectrum (1145–1720 Å) of the distant quasar Q 0302–003 (z = 3.286) was observed at 1.8 Å resolution during 10 orbits of the Hubble Space Telescope with the Space Telescope Imaging Spectrograph. A total integration time of 23,280 s was obtained. The spectrum clearly delineates the Gunn-Peterson He II absorption trough, produced by He II Lyα along the line of sight over the redshift range z = 2.78 − 3.28. Interpretation of the results was facilitated by modeling based on Keck HIRES spectra of the

AIP Conference Proceedings, 1997

Symposium - International Astronomical Union, 2000

Astronomy and Astrophysics, Aug 30, 1994

Astronomy and Astrophysics, 1992

University of Groningen Thesis 1992, Aug 30, 1992

AIP Conference Proceedings, 1989

Hst Proposal, Jul 1, 2000

Nato Asib Proc 105 White Dwarfs, 2003