15,888 research outputs found
Improved method of optical design
Optical system designed by third order aberration theory is significantly improved by placing it into a ray deviation design program composed of two distinct computer programs. Tests were conducted on telescope systems, an ultraviolet relay lens, and a four lens corrector system
General optics evaluation program (GENOPTICS)
Program prints and plots results of computations such as ray traces, radial energy distributions, and designs of two-mirror telescopes
Ray tracing program with options for diffraction gratings
Diffraction theory, developed in vectorial form and coded into ray tracing routines, permits tracing rays of any wavelength through surfaces that are plane, spherical, conical, or aspheric polynomial. Ruled diffraction gratings may run in either X-direction or Y-direction, where Z is optical axis
How Evolved are the Mass Donor Stars inCataclysmic Variables?
Recent spectroscopic observations have identified several cataclysmic
variables non-solar metal abundances. We present theoretical models which
examine the level of core evolution expected for CV secondaries prior to
contact. Our results indicate that few secondary stars evolve past 10% of their
main sequence lifetime prior to the initiation of mass transfer; a result which
is in agreement with present day observations. Thus, the non-solar metal
abundances observed must be due to nuclear burning by-products accreted by the
secondary star during common envelope sweeping prior to initial contact or
ejecta collected during classical nova outbursts.Comment: To Appear in PAS
Fringe Science: Defringing CCD Images with Neon Lamp Flat Fields
Fringing in CCD images is troublesome from the aspect of photometric quality
and image flatness in the final reduced product. Additionally, defringing
during calibration requires the inefficient use of time during the night to
collect and produce a "supersky" fringe frame. The fringe pattern observed in a
CCD image for a given near-IR filter is dominated by small thickness variations
across the detector with a second order effect caused by the wavelength extent
of the emission lines within the bandpass which produce the interference
pattern. We show that essentially any set of emission lines which generally
match the wavelength coverage of the night sky emission lines within a bandpass
will produce an identical fringe pattern. We present an easy, inexpensive, and
efficient method which uses a neon lamp as a flat field source and produces
high S/N fringe frames to use for defringing an image during the calibration
process.Comment: accepted to PAS
ST/STIS Spectroscopy of the White Dwarfs in the Short-Period Dwarf Novae LL And and EF Peg
We present new HST/STIS observations of the short-period dwarf novae LL And
and EF Peg during deep quiescence. We fit stellar models to the UV spectra and
use optical and IR observations to determine the physical parameters of the
whitedwarfs in the systems, the distances to the binaries, and the properties
of thesecondary stars. Both white dwarfs are relatively cool, having T_{eff}
near 15000K, and consistent with a mass of 0.6 M-sun. The white dwarf in LL And
appears to be of solar abundance or slightly lower while that in EF Peg is near
0.1-0.3 solar. LL And is found to be 760 pc away while EF Peg is closer at 380
pc. EF Peg appears to have an ~M5V secondary star, consistent with that
expected for its orbital period, while the secondary object in LL And remains a
mystery.Comment: Accepted in Ap
Spectroscopic Observations of Twenty-one Faint Cataclysmic Variables Candidates
We provide the first minimum light spectroscopic observations for 21
previously known or suspected faint cataclysmic variable candidates. The
sources were selected from the Downes et al. (2001) living edition catalog and
the identified candidates have minimum light magnitudes of V~18-22. We confirm
15 of the candidates to be cataclysmic variables.Comment: 10 pages, 4 figures, accepted by A&
The Densities of Planets in Multiple Stellar Systems
We analyze the effect of companion stars on the bulk density of 29 planets
orbiting 15 stars in the Kepler field. These stars have at least one stellar
companion within 2", and the planets have measured masses and radii, allowing
an estimate of their bulk density. The transit dilution by the companion star
requires the planet radii to be revised upward, even if the planet orbits the
primary star; as a consequence, the planetary bulk density decreases. We find
that, if planets orbited a faint companion star, they would be more
volatile-rich, and in several cases their densities would become
unrealistically low, requiring large, inflated atmospheres or unusually large
mass fractions in a H/He envelope. In addition, for planets detected in radial
velocity data, the primary star has to be the host. We can exclude 14 planets
from orbiting the companion star; the remaining 15 planets in seven planetary
systems could orbit either the primary or the secondary star, and for five of
these planets the decrease in density would be substantial even if they orbited
the primary, since the companion is of almost equal brightness as the primary.
Substantial follow-up work is required in order to accurately determine the
radii of transiting planets. Of particular interest are small, rocky planets
that may be habitable; a lower mean density might imply a more volatile-rich
composition. Reliable radii, masses, and thus bulk densities will allow us to
identify which small planets are truly Earth-like.Comment: Accepted by AJ; 22 page
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