52 research outputs found
Possible detection of singly-ionized oxygen in the Type Ia SN 2010kg
We present direct spectroscopic modeling of 11 high-S/N observed spectra of
the Type Ia SN 2010kg, taken between -10 and +5 days with respect to B-maximum.
The synthetic spectra, calculated with the SYN++ code, span the range between
4100 and 8500 \r{A}. Our results are in good agreement with previous findings
for other Type Ia SNe. Most of the spectral features are formed at or close to
the photosphere, but some ions, like Fe II and Mg II, also form features at
~2000 - 5000 km s above the photosphere. The well-known high-velocity
features of the Ca II IR-triplet as well as Si II 6355 are also
detected.
The single absorption feature at ~4400 \r{A}, which usually has been
identified as due to Si III, is poorly fit with Si III in SN 2010kg. We find
that the fit can be improved by assuming that this feature is due to either C
III or O II, located in the outermost part of the ejecta, ~4000 - 5000 km
s above the photosphere. Since the presence of C III is unlikely,
because of the lack of the necessary excitation/ionization conditions in the
outer ejecta, we identify this feature as due to O II. The simultaneous
presence of O I and O II is in good agreement with the optical depth
calculations and the temperature distribution in the ejecta of SN 2010kg. This
could be the first identification of singly ionized oxygen in a Type Ia SN
atmosphere.Comment: Submitted to MNRA
Optical Spectra of 73 Stripped-Envelope Core-Collapse Supernovae
We present 645 optical spectra of 73 supernovae (SNe) of Types IIb, Ib, Ic,
and broad-lined Ic. All of these types are attributed to the core collapse of
massive stars, with varying degrees of intact H and He envelopes before
explosion. The SNe in our sample have a mean redshift = 4200 km/s. Most of
these spectra were gathered at the Harvard-Smithsonian Center for Astrophysics
(CfA) between 2004 and 2009. For 53 SNe, these are the first published spectra.
The data coverage range from mere identification (1-3 spectra) for a few SNe to
extensive series of observations (10-30 spectra) that trace the spectral
evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73
SNe presented here, we have well-determined dates of maximum light to determine
the phase of each spectrum. Our sample constitutes the most extensive spectral
library of stripped-envelope SNe to date. We provide very early coverage (as
early as 30 days before V-band max) for photospheric spectra, as well as
late-time nebular coverage when the innermost regions of the SNe are visible
(as late as 2 years after explosion, while for SN1993J, we have data as late as
11.6 years). This data set has homogeneous observations and reductions that
allow us to study the spectroscopic diversity of these classes of stripped SNe
and to compare these to SNe associated with gamma-ray bursts. We undertake
these matters in follow-up papers.Comment: Published by the Astronomical Journal in May 2015. All spectra are
publicly available at the CfA SN archive:
http://www.cfa.harvard.edu/supernova/SNarchive.html . A companion paper on
constructing SNID templates based on these spectra is by Liu & Modjaz (2014)
and the resulting SNID templates are available from the NYU website:
http://cosmo.nyu.edu/SNYU/spectra
Multi-color Optical and NIR Light Curves of 64 Stripped-Envelope Core-Collapse Supernovae
We present a densely-sampled, homogeneous set of light curves of 64 low
redshift (z < 0.05) stripped-envelope supernovae (SN of type IIb, Ib, Ic and
Ic-bl). These data were obtained between 2001 and 2009 at the Fred L. Whipple
Observatory (FLWO) on Mt. Hopkins in Arizona, with the optical FLWO 1.2-m and
the near-infrared PAIRITEL 1.3-m telescopes. Our dataset consists of 4543
optical photometric measurements on 61 SN, including a combination of UBVRI,
UBVr'i', and u'BVr'i', and 2142 JHKs near-infrared measurements on 25 SN. This
sample constitutes the most extensive multi-color data set of stripped-envelope
SN to date. Our photometry is based on template-subtracted images to eliminate
any potential host galaxy light contamination. This work presents these
photometric data, compares them with data in the literature, and estimates
basic statistical quantities: date of maximum, color, and photometric
properties. We identify promising color trends that may permit the
identification of stripped-envelope SN subtypes from their photometry alone.
Many of these SN were observed spectroscopically by the CfA SN group, and the
spectra are presented in a companion paper (Modjaz et al. 2014). A thorough
exploration that combines the CfA photometry and spectroscopy of
stripped-envelope core-collapse SN will be presented in a follow-up paper.Comment: 26 pages, 17 figures, 8 tables. Revised version resubmitted to ApJ
Supplements after referee report. Additional online material is available
through http://cosmo.nyu.edu/SNYU
Discovery of a Wolf-Rayet Star Through Detection of its Photometric Variability
We report the serendipitous discovery of a heavily reddened Wolf-Rayet star
that we name WR142b. While photometrically monitoring a cataclysmic variable,
we detected weak variability in a nearby field star. Low-resolution
spectroscopy revealed a strong emission line at 7100 Ang., suggesting an
unusual object and prompting further study. A spectrum taken with the
Hobby-Eberly Telescope confirms strong HeII emission and a NIV 7112 Ang. line
consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis
of the HeII line strengths reveals no detectable hydrogen in WR142b. A
blue-sensitive spectrum obtained with the Large Binocular Telescope shows no
evidence for a hot companion star. The continuum shape and emission line ratios
imply a reddening of E(B-V)=2.2 to 2.5 mag. If not for the dust extinction,
this new Wolf-Rayet star could be visible to the naked eye.Comment: 15 pages, 6 figures, submitted to the Astronomical Journa
A decision exercise to engage cancer patients and families in Deliberation about Medicare Coverage for advanced Cancer Care
BACKGROUND: Concerns about unsustainable costs in the US Medicare program loom as the number of retirees increase and experiences serious and costly illnesses like cancer. Engagement of stakeholders, particularly cancer patients and their families, in prioritizing insured services offers a valuable strategy for informing Medicare coverage policy. We designed and evaluated a decision exercise that allowed cancer patients and family members to choose Medicare benefits for advanced cancer patients. METHODS: The decision tool, Choosing Health plans All Together (CHAT) was modified to select services for advanced cancer patients. Patients with a cancer history (N = 246) and their family members (N = 194) from North Carolina participated in 70 CHAT sessions. Variables including participants’ socio-demographic characteristics, health status, assessments of the exercise and results of group benefit selections were collected. Routine descriptive statistics summarized participant characteristics and Fisher’s exact test compared group differences. Qualitative analysis of group discussions were used to ascertain reasons for or against selecting benefits. RESULTS: Patients and family members (N = 440) participated in 70 CHAT exercises. Many groups opted for such services as palliative care, nursing facilities, and services not currently covered by the Medicare program. In choosing among four levels of cancer treatment coverage, no groups chose basic coverage, 27 groups (39%) selected intermediate coverage, 39 groups (56%) selected high coverage, and 4 groups (6%) chose the most comprehensive cancer coverage. Reasons for or against benefit selection included fairness, necessity, need for prioritizing, personal experience, attention to family needs, holistic health outlook, preference for comfort, freedom of choice, and beliefs about the proper role of government. Participants found the exercise very easy (59%) or fairly easy (39%) to understand and very informative (66%) or fairly informative (31%). The majority agreed that the CHAT exercise led to fair decisions about priorities for coverage by which they could abide. CONCLUSIONS: It is possible to involve cancer patients and families in explicit discussions of their priorities for affordable advanced cancer care through the use of decision tools designed for this purpose. A key question is whether such a conversation is possible on a broader, national level
Type IIb Supernova SN 2011dh: Spectra and Photometry from the Ultraviolet to the Near-Infrared
We report spectroscopic and photometric observations of the Type IIb SN
2011dh obtained between 4 and 34 days after the estimated date of explosion
(May 31.5 UT). The data cover a wide wavelength range from 2,000 Angstroms in
the UV to 2.4 microns in the NIR. Optical spectra provide line profiles and
velocity measurements of HI, HeI, CaII and FeII that trace the composition and
kinematics of the SN. NIR spectra show that helium is present in the atmosphere
as early as 11 days after the explosion. A UV spectrum obtained with the STIS
reveals that the UV flux for SN 2011dh is low compared to other SN IIb. The HI
and HeI velocities in SN 2011dh are separated by about 4,000 km/s at all
phases. We estimate that the H-shell of SN 2011dh is about 8 times less massive
than the shell of SN 1993J and about 3 times more massive than the shell of SN
2008ax. Light curves (LC) for twelve passbands are presented. The maximum
bolometric luminosity of erg s occurred
about 22 days after the explosion. NIR emission provides more than 30% of the
total bolometric flux at the beginning of our observations and increases to
nearly 50% of the total by day 34. The UV produces 16% of the total flux on day
4, 5% on day 9 and 1% on day 34. We compare the bolometric light curves of SN
2011dh, SN 2008ax and SN 1993J. The LC are very different for the first twelve
days after the explosions but all three SN IIb display similar peak
luminosities, times of peak, decline rates and colors after maximum. This
suggests that the progenitors of these SN IIb may have had similar compositions
and masses but they exploded inside hydrogen shells that that have a wide range
of masses. The detailed observations presented here will help evaluate
theoretical models for this supernova and lead to a better understanding of SN
IIb.Comment: 23 pages, 14 figures, 9 tables, accepted by Ap
Type II Supernovae as Probes of Cosmology
- Constraining the cosmological parameters and understanding Dark Energy have
tremendous implications for the nature of the Universe and its physical laws.
- The pervasive limit of systematic uncertainties reached by cosmography
based on Cepheids and Type Ia supernovae (SNe Ia) warrants a search for
complementary approaches.
- Type II SNe have been shown to offer such a path. Their distances can be
well constrained by luminosity-based or geometric methods. Competing,
complementary, and concerted efforts are underway, to explore and exploit those
objects that are extremely well matched to next generation facilities.
Spectroscopic follow-up will be enabled by space- based and 20-40 meter class
telescopes.
- Some systematic uncertainties of Type II SNe, such as reddening by dust and
metallicity effects, are bound to be different from those of SNe Ia. Their
stellar progenitors are known, promising better leverage on cosmic evolution.
In addition, their rate - which closely tracks the ongoing star formation rate
- is expected to rise significantly with look- back time, ensuring an adequate
supply of distant examples.
- These data will competitively constrain the dark energy equation of state,
allow the determination of the Hubble constant to 5%, and promote our
understanding of the processes involved in the last dramatic phases of massive
stellar evolution.Comment: Science white paper, submitted to the Decadal committee Astro201
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