418 research outputs found
Alien Registration- Levesque, John (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/29054/thumbnail.jp
Circumstellar dust as a solution to the red supergiant supernova progenitor problem
We investigate the red supergiant problem: the apparent dearth of Type IIP
supernova progenitors with masses between 16 and 30 M_sun. Although red
supergiants with masses in this range have been observed, none have been
identified as progenitors in pre-explosion images. We show that by failing to
take into account the additional extinction resulting from the dust produced in
the red supergiant winds, we risk underestimating the luminosity of the most
massive red supergiants at the end of their lives. We estimate the initial
masses of all Type IIP progenitors for which observations exist and analyse the
resulting population. We find that the most likely maximum mass for a Type IIP
progenitor is 21^{+2}_{-1} M_sun. This is in closer agreement with the limit
predicted from single star evolution models.Comment: 10 pages, 6 figures and 4 tables. Accepted for publication in MNRA
Long and Short Duration Exposures to the Selective Serotonin Reuptake Inhibitors (SSRIs) Fluoxetine, Paroxetine and Sertraline at Environmentally Relevant Concentrations Lead to Adverse Effects on Zebrafish Behaviour and Reproduction
Selective serotonin reuptake inhibitors (SSRIs) are currently the most prescribed class of psychotropic medications. Their increased global manufacture and use have become growing concerns for aquatic toxicologists and environmental biologists, who assess both the direct and indirect effects of substances on the environment and on human health. In order to assess the potential impact of environmentally relevant levels of SSRIs on fish development, behaviour and reproduction, we exposed juvenile and adult zebrafish to a select group of SSRIs using two separate exposure paradigms. In the first paradigm, juvenile zebrafish were exposed to Fluoxetine (Prozac), Paroxetine (Paxil), Sertraline (Zoloft) or a mixture of the three beginning at environmentally relevant levels (10 µg/L) for 135 days (long-term exposure) beginning at 5 days post fertilization (dpf). In the second paradigm, adult zebrafish were exposed to matching concentrations of the same SSRIs for 35 days (short-term exposure). The long-term exposure paradigm proved to have little to no overt effect on growth or development at sub-lethal concentrations (10 and 100 µg/L). However, both the stress/anxiety response (novel tank tests) and reproduction (fecundity and fertility) were dramatically reduced. Importantly, the short-term exposure of reproductively mature fish led to similar adverse effects on both the stress response and reproduction. Following both the short and long duration exposure paradigms, a 2-week washout period led to a small reduction in the adverse effects. These findings highlight the potential for SSRIs to negatively impact population dynamics in zebrafish and may be of particular value should they be found in other fish species in the environment
Software Implements a Space-Mission File-Transfer Protocol
CFDP is a computer program that implements the CCSDS (Consultative Committee for Space Data Systems) File Delivery Protocol, which is an international standard for automatic, reliable transfers of files of data between locations on Earth and in outer space. CFDP administers concurrent file transfers in both directions, delivery of data out of transmission order, reliable and unreliable transmission modes, and automatic retransmission of lost or corrupted data by use of one or more of several lost-segment-detection modes. The program also implements several data-integrity measures, including file checksums and optional cyclic redundancy checks for each protocol data unit. The metadata accompanying each file can include messages to users application programs and commands for operating on remote file systems
HST/NICMOS observations of the GLIMPSE9 stellar cluster
We present HST/NICMOS photometry, and low-resolution K-band spectra of the
GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a
cluster sequence with H-Ks =1 mag, indicating an interstellar extinction
Aks=1.6\pm0.2 mag. The spectra of the three brightest stars show deep CO
band-heads, which indicate red supergiants with spectral type M1-M2. Two 09-B2
supergiants are also identified, which yield a spectrophotometric distance of
4.2\pm0.4 kpc. Presuming that the population is coeval, we derive an age
between 15 and 27 Myr, and a total cluster mass of 1600\pm400 Msun, integrated
down to 1 Msun. In the vicinity of GLIMPSE9 are several HII regions and SNRs,
all of which (including GLIMPSE 9) are probably associated with a giant
molecular cloud (GMC) in the inner galaxy. GLIMPSE9 probably represents one
episode of massive star formation in this GMC. We have identified several other
candidate stellar clusters of the same complex.Comment: 13 pages, 14 figures. accepted for publication in ApJ. A version with
high-resolution figures can be found at the following location
ftp://ftp.rssd.esa.int/pub/mmessine/ms.pdf New version with updated
reference
The red supergiants & Wolf-Rayet stars of NGC 604
We study the post-main sequence stars in NGC 604, the most luminous HII
region in M33. Previously, a number of Wolf-Rayet (WR) stars and one red
supergiant (RSG) have been discovered. Based on broadband photometry of the
region, we present evidence that is consistent with the presence of this RSG
and with three more RSG candidates. Using SED fitting based on HST UVIJHK
photometry we estimate the ages of the WR stars and RSGs finding that the two
populations are from distinct formation episodes with ages 3.2\pm\pm$ 0.6) x
10^5Msun. We find a large discrepancy between the expected H{\alpha} flux from
such a massive cluster and that one observed. This suggests that 49 (+16,-19)
percent of the ionizing photons produced by massive stars in NGC 604 is leaking
from this HII region. We also suggest that the implications of an old RSG
population mean that if NGC 604 was more distant and only observed in the
infrared (IR) it would be difficult to study the youngest burst of star
formation due to the contamination of RSGs.Comment: Accepted for publication in MNRAS, 13 pages, 10 figures, 3 table
Spectroscopic Discovery of the Broad-Lined Type Ic Supernova 2010bh Associated with the Low-Redshift GRB 100316D
We present the spectroscopic discovery of a broad-lined Type Ic supernova (SN
2010bh) associated with the nearby long-duration gamma-ray burst (GRB) 100316D.
At z = 0.0593, this is the third-nearest GRB-SN. Nightly optical spectra
obtained with the Magellan telescopes during the first week after explosion
reveal the gradual emergence of very broad spectral features superposed on a
blue continuum. The supernova features are typical of broad-lined SNe Ic and
are generally consistent with previous supernovae associated with low-redshift
GRBs. However, the inferred velocities of SN 2010bh at 21 days after explosion
are a factor of ~2 times larger than those of the prototypical SN 1998bw at
similar epochs, with v ~ 26,000 km/s, indicating a larger explosion energy or a
different ejecta structure. A near-infrared spectrum taken 13.8 days after
explosion shows no strong evidence for He I at 1.083 microns, implying that the
progenitor was largely stripped of its helium envelope. The host galaxy is of
low luminosity (M_R ~ -18.5 mag) and low metallicity (Z < 0.4 Z_solar), similar
to the hosts of other low-redshift GRB-SNe.Comment: 6 pages, 4 figures, 1 table, submitted to ApJ Letter
- …