311 research outputs found
Contamination of spectroscopic observations by satellite constellations
The number of satellites on low orbit has dramatically increased over the
past years, raising concerns among the astronomical community about their
impact on observations. Spectroscopic observations represent a large fraction
of professional data, and spectrographs lack spatial information that can
reveal the presence of a satellite. We simulated how often satellites
contaminate spectrograph observations by using realistic constellations with
over 400,000 objects. We also measured how a spectrum is affected by using real
data from different scientific targets and a scaled solar analogue as the
satellite, and using standard tools to measure astrophysical parameters and
compare them with the clean spectrum. The fraction of affected spectra varies
dramatically with the elevation of the sun, with a maximum of 10% at twilight
and a nightly average of about 2%. Because of the fast motion of the satellites
and the limiting magnitude of the spectrographs, high-resolution instruments
are essentially blind to most satellites. For lower resolution spectrographs,
the effect on the measured astrophysical parameters depends strongly on the
signal-to-noise of the exposure, longer exposures on brighter targets being the
least affected at <=1%. Satellites that are brighter and/or higher than the
constellation satellites, while less numerous, can also contaminate spectra.
While the fraction of affected spectra is likely to remain low, some of these
contaminated spectra will be difficult to identify, as it is already the case
with existing satellites and asteroids. The best mitigation is to ensure that
their brightness is fainter than V=7, that their absolute magnitude V1000km is
also fainter than 7, and, whenever possible, to shoot multiple exposures.Comment: accepted for publication in A&
Analysis of the possible satellite contamination in LAMOST-MRS spectra
We present the detection of false positive double-lined spectroscopic
binaries candidates (SB2) using medium-resolution survey (MRS) spectra from the
one time-domain field of LAMOST data release 10 (DR10). The secondary component
in all these binaries has near zero radial velocity and solar-like spectral
lines. Highly likely this is light from the semi-transparent clouds illuminated
by the full Moon. However we also suspect that partially this contamination can
be caused by a solar light reflected from the surface of low-orbital artificial
satellites launched in the beginning of 2022. We found several possible
contaminant candidates using archival orbital data. We propose measures to
reduce risk of such contamination for the future observations and methods to
find it in archived ones.Comment: accepted in MNRAS letters 2023 July 0
Low Prevalence of TP53 Mutations and MDM2 Amplifications in Pediatric Rhabdomyosarcoma
The tumor suppressor gene TP53 is the most commonly mutated gene in human cancer. The reported prevalence of mutations in rhabdomyosarcoma (RMS) varies widely, with recent larger studies suggesting that TP53 mutations in pediatric RMS may be extremely rare. Overexpression of MDM2 also attenuates p53 function. We have performed TP53 mutation/MDM2 amplification analyses in the largest series analyzed thus far, including DNA isolated from 37 alveolar and 38 embryonal RMS tumor samples obtained from the Cooperative Human Tissue Network (CHTN). Available samples were frozen tumor tissues (N = 48) and histopathology slides. TP53 mutations in exons 4–9 were analyzed by direct sequencing in all samples, and MDM2 amplification analysis was performed by differential PCR on a subset of 22 samples. We found only one sample (1/75, 1.3%) carrying a TP53 mutation at codon 259 (p.D259Y) and no MDM2 amplification. Two SNPs in the TP53 pathway, associated with accelerated tumor onset in germline TP53 mutation carriers, (TP53 SNP72 (rs no. 1042522) and MDM2 SNP309 (rs no. 2279744)), were not found to confer earlier tumor onset. In conclusion, we confirm the extremely low prevalence of TP53 mutations/MDM2 amplifications in pediatric RMS (1.33% and 0%, respectively). The possible inactivation of p53 function by other mechanisms thus remains to be elucidated
Isotopic ratios in outbursting comet C/2015 ER61
Isotopic ratios in comets are critical to understanding the origin of
cometary material and the physical and chemical conditions in the early solar
nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total
brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp
increase in brightness offered a rare opportunity to measure the isotopic
ratios of the light elements in the coma of this comet. We obtained two
high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017
April 13 and 17. At the time of our observations, the comet was fading
gradually following the outburst. We measured the nitrogen and carbon isotopic
ratios from the CN violet (0,0) band and found that C/C=100
15, N/N=130 15. In addition, we determined the
N/N ratio from four pairs of NH isotopolog lines and measured
N/N=140 28. The measured isotopic ratios of C/2015 ER61 do
not deviate significantly from those of other comets.Comment: 4 pages, 4 figures, accepted to be published by A&
Fitting the Light Curve of 1I/`Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques
In this paper, we investigate the nonprincipal axis (NPA) rotational state of
1I/`Oumuamua -- the first interstellar object discovered traversing the inner
Solar System -- from its photometric light curve. Building upon Mashchenko
(2019), we develop a model which incorporates NPA rotation and {Sun-induced,
time-varying} outgassing torques to generate synthetic light curves of the
object. The model neglects tidal forces, which are negligible compared to
outgassing torques over the distances that `Oumuamua was observed. We implement
an optimization scheme that incorporates the NPA rotation model to calculate
the initial rotation state of the object. We find that an NPA rotation state
with an average period of hr best reproduces the
photometric data. The discrepancy between this period and previous estimates is
due to continuous period modulation induced by outgassing torques in the
rotational model, {as well as different periods being used}. The best fit to
the October 2017 data does not reproduce the November 2017 data (although the
later measurements are too sparse to fit). The light curve is consistent with
no secular evolution of the angular momentum, somewhat in tension with the
empirical correlations between nuclear spin-up and cometary outgassing. The
complex rotation of `Oumuamua may be {the result of primordial rotation about
the smallest principal axis} if (i) the object experienced hypervolatile
outgassing and (ii) our idealized outgassing model is accurate.Comment: 22 pages, 8 figures, 1 animation. Accepted to the Planetary Science
Journal. The animation can be found on YouTube (https://youtu.be/f5YEAMTvIeo)
and in the online publication by PSJ (when available
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