arXiv subjects

Cherie L. Miskey

Publications and source records attributed to Cherie L. Miskey.

3 recordsLinked to original sources

arXiv2003

STIS Spectral Imagery of the OB Stars in NGC 604: Describing the Extraction Technique for a Crowded Stellar Field

We have developed a data reduction procedure to extract multiple spectra from a single two-dimensional Space Telescope Imaging Spectrograph (STIS) image of a crowded stellar field. This paper provides a description of our new technique, utilizing a STIS ultraviolet spectral image, acquired with the G140L grating and the 52 arcsec x 2 arcsec aperture, sampling a concentration of O and B stars in the central region of the NGC 604 starburst in M33. The software routines can disentangle and produce reliable ultraviolet spectra of stars with angular separations as small as 0.055 arcsec. Use of the extraction slit, based upon our model of the spectral cross dispersion profile, generates spectra with slightly higher resolution than the STScI standard processing. Our results clearly show that the spectral imaging capability of STIS represents a powerful tool for studying luminous stars in the star-forming regions of the Local Group.

astro-ph↗

arXiv2003

STIS Spectral Imagery of the OB Stars in NGC 604: The Most Luminous Stars

We present results using 2-D spectral imagery and photometry obtained with the Hubble Space Telescope (HST) for the starburst H II region, NGC 604, in nearby galaxy M33. The spectral imagery was acquired with the Space Telescope Imaging Spectrograph (STIS) using the MAMA/G140L configuration, spanning 1170-1730 A. From a single 1720 sec STIS exposure, we extracted spectra for 49 stars and derived individual UV spectral types for 40 stars in the crowded 25"x2" stellar field. These stars represent a significant fraction of the young, luminous O and B stars. Three objects have pronounced He II 1640 emission, the signature of W-R or luminous Of stars. By combining UV fluxes with WFPC and WFPC2 visual photometry, we derive the extinction curve for NGC 604. We use this curve, the distance for M33, derived UV spectral types, and HST photometry, to determine positions of these stars in the upper H-R diagram. The revised O star effective temperature scale (Martins et al.) is essential in obtaining reliable positions in the log(L*)-log(T(eff)) plane. These stars are quite young with an age of ~3 Myr. The spectra and photometry indicate three exceedingly luminous objects. Their inferred locations in the H-R diagram indicate stellar masses > 120 solar masses. High spatial resolution HST imagery provides no evidence of multiple stars composing these objects. Still we cannot eliminate the possibility that they are unresolved multiple stars of lower mass, possibly W-R stars. Tests demonstrate that the ten most luminous stars predominantly determine the UV spectral features seen in the total light of NGC 604. We conclude that interpretation of spectral fitting of more distant starburst galaxies, where individual stars are not resolved, must be done with extreme care.

astro-ph↗

arXiv2002

Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with the Hubble Space Telescope WPFC2

(abridged) We present the discovery of two T dwarf binaries, 2MASS 1225-2739AB and 2MASS 1534-2952AB, identified in a sample of ten T dwarfs imaged with the Hubble Space Telescope Wide Field Planetary Camera 2. The separations of the two binary systems are 0{\farcs}282$\pm$0{\farcs}005 and 0{\farcs}065$\pm$0{\farcs}007, implying projected separations of 3.17$\pm$0.14 and 1.0$\pm$0.3 AU, respectively. The observed binary fraction of our HST sample, 20$^{+17}_{-7}$%, is consistent with results obtained for late-M and L field dwarfs, and implies a bias-corrected binary fraction of 9$^{+15}_{-4}$% for $a \gtrsim 1$ AU and $q \gtrsim 0.4$, significantly lower than the binary fractions of F--G and early-type M dwarf stars. Neither of the T binaries have separations $a \gtrsim 10$ AU, consistent with results from other brown dwarf binary searches. We conclude that tidal disruption by passing stars or Giant Molecular Clouds, which limits the extent of wide stellar binaries, plays no role in eliminating wide brown dwarf binaries, implying either disruption very early in the formation process (ages $\lesssim 1-10$ Myr) or a formation mechanism which precludes such systems. We find that the maximum binary separation in the brown dwarf regime appears to scale as M$_{total}^2$, a possible clue to the physical mechanism which restricts wide substellar systems.

astro-ph↗