82 research outputs found
Some Bright Stars with Smooth Continua for Calibrating the Response of High Resolution Spectrographs
When characterizing a high resolution echelle spectrograph, for instance for
precise Doppler work, it is useful to observe featureless sources such as
quartz lamps or hot stars to determine the response of the instrument. Such
sources provide a way to determine the blaze function of the orders,
pixel-to-pixel variations in the detector, fringing in the system, and other
important characteristics. In practice, however, many B or early A stars do not
provide a smooth continuum, whether because they are not rotating rapidly
enough or for some other reason. In fact, we have found that published
rotational velocities and temperatures are not a specific and sensitive guide
to whether a star's continuum will be smooth. A useful resource for observers,
therefore, is a list of "good" hot stars: bright, blue stars known empirically
to have no lines or other spectral features beyond the Balmer series with
minima below 95% of the continuum.
We have compiled a list of such stars visible from Northern Hemisphere
telescopes. This list includes all stars listed in the Yale Bright Star Catalog
(Hoffleit & Jaschek 1991) as being single with V 175 km/s, and
declination > -30, and many other hot stars that we have found useful for
calibration purposes.
The list here of "bad" stars may also be of interest in studies of hot,
slowly rotating stars
On the Transit Potential of the Planet Orbiting iota Draconis
Most of the known transiting exoplanets are in short-period orbits, largely
due to the bias inherent in detecting planets through the transit technique.
However, the eccentricity distribution of the known radial velocity planets
results in many of those planets having a non-negligible transit probability.
One such case is the massive planet orbiting the giant star iota Draconis, a
situation where both the orientation of the planet's eccentric orbit and the
size of the host star inflate the transit probability to a much higher value
than for a typical hot Jupiter. Here we present a revised fit of the radial
velocity data with new measurements and a photometric analysis of the stellar
variability. We provide a revised transit probability, an improved transit
ephemeris, and discuss the prospects for observing a transit of this planet
from both the ground and space.Comment: 6 pages, 7 figures, accepted for publication in ApJ. Radial
velocities will be made available in the on-line version and through the NASA
Star and Exoplanet Database (NStED). Minor corrections from ApJ proof have
been applie
Late-Time Circumstellar Interaction in a Spitzer Selected Sample of Type IIn Supernovae
Type IIn supernovae (SNe IIn) are a rare (< 10%) subclass of core-collapse
SNe that exhibit relatively narrow emission lines from a dense, pre-existing
circumstellar medium (CSM). In 2009, a warm Spitzer survey observed 30 SNe IIn
discovered in 2003 - 2008 and detected 10 SNe at distances out to 175 Mpc with
unreported late-time infrared emission, in some cases more than 5 years
post-discovery. For this single epoch of data, the warm-dust parameters suggest
the presence of a radiative heating source consisting of optical/X-ray emission
continuously generated by ongoing CSM interaction. Here we present
multi-wavelength follow-up observations of this sample of 10 SNe IIn and the
well-studied Type IIn SN 2010jl. A recent epoch of Spitzer observations reveals
ongoing mid-infrared emission from nine of the SNe in this sample. We also
detect three of the SNe in archival WISE data, in addition to SNe 1987A,
2004dj, and 2008iy. For at least five of the SNe in the sample, optical and/or
X-ray emission confirms the presence of radiative emission from ongoing CSM
interaction. The two Spitzer nondetections are consistent with the forward
shock overrunning and destroying the dust shell, a result that places upper
limits on the dust-shell size. The optical and infrared observations confirm
the radiative heating model and constrain a number of model parameters,
including progenitor mass-loss characteristics. All of the SNe in this sample
experienced an outburst on the order of tens to hundreds of years prior to the
SN explosion followed by periods of less intense mass loss. Although all
evidence points to massive progenitors, the variation in the data highlights
the diversity in SN IIn progenitor evolution. While these observations do not
identify a particular progenitor system, they demonstrate that future,
coordinated, multi-wavelength campaigns can constrain theoretical mass-loss
models.Comment: 10 pages, 6 figures, accepted to AJ (with comments
Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days
We present an optical nebular spectrum of the nearby Type Ia supernova
2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution
since the +593 day optical spectrum, but there are several curious aspects in
this new extremely late-time regime. We suggest that the persistence of the
~\AA\ feature is due to Na I D, and that a new emission feature at
~\AA\ may be [Ca II]. Also, we discuss whether the new emission
feature at ~\AA\ might be [Fe I] or the high-velocity hydrogen
predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear
velocity evolution of per 100 days from at least
+220 to +980 days, but the line's shape also changes in this time, suggesting
that line blending contributes to the evolution. At days after
explosion, flux from the SN has declined to a point where contribution from a
luminous secondary could be detected. In this work we make the first
observational tests for a post-impact remnant star and constrain its
temperature and luminosity to and
. Additionally, we do not see any evidence for narrow H
emission in our spectrum. We conclude that observations continue to strongly
exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA
On the Progenitor System of the Type Iax Supernova 2014dt in M61
We present pre-explosion and post-explosion Hubble Space Telescope images of
the Type Iax supernova (SN Iax) 2014dt in M61. After astrometrically aligning
these images, we do not detect any stellar sources at the position of the SN in
the pre-explosion images to relatively deep limits (3 sigma limits of M_F438W >
-5.0 mag and M_F814W > -5.9 mag). These limits are similar to the luminosity of
SN 2012Z's progenitor system (M_F435W = -5.43 +/- 0.15 and M_F814W = -5.24 +/-
0.16 mag), the only probable detected progenitor system in pre-explosion images
of a SN Iax, and indeed, of any white dwarf supernova. SN 2014dt is consistent
with having a C/O white-dwarf primary/helium-star companion progenitor system,
as was suggested for SN 2012Z, although perhaps with a slightly smaller or
hotter donor. The data are also consistent with SN 2014dt having a low-mass red
giant or main-sequence star companion. The data rule out main-sequence stars
with M_init > 16 M_sun and most evolved stars with M_init > 8 M_sun as being
the progenitor of SN 2014dt. Hot Wolf-Rayet stars are also allowed, but the
lack of nearby bright sources makes this scenario unlikely. Because of its
proximity (D = 12 Mpc), SN 2014dt is ideal for long-term monitoring, where
images in ~2 years may detect the companion star or the luminous bound remnant
of the progenitor white dwarf.Comment: 5 pages, 3 figures, submitted to ApJ
The Progenitor of Supernova 2011dh Has Vanished
We conducted Hubble Space Telescope (HST) Snapshot observations of the Type
IIb Supernova (SN) 2011dh in M51 at an age of ~641 days with the Wide Field
Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN
HST images, has disappeared, implying that this star was almost certainly the
progenitor of the SN. Interpretation of the early-time SN data which led to the
inference of a compact nature for the progenitor, and to the expected survival
of this yellow supergiant, is now clearly incorrect. We also present
ground-based UBVRI light curves obtained with the Katzman Automatic Imaging
Telescope (KAIT) at Lick Observatory up to SN age ~70 days. From the
light-curve shape including the very late-time HST data, and from recent
interacting binary models for SN 2011dh, we estimate that a putative surviving
companion star to the now deceased yellow supergiant could be detectable by
late 2013, especially in the ultraviolet. No obvious light echoes are
detectable yet in the SN environment.Comment: 6 pages, new versions of the 3 figures, improved U-band SN
photometry, to appear in ApJ Letter
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