144 research outputs found
A Spectral Classification System for Hydrogen-deficient Carbon Stars
Stellar spectral classification, and especially the Yerkes system, has been
highly useful in the study of stars. While there is a currently accepted
classification system for carbon stars, the subset of Hydrogen-deficient Carbon
(HdC) stars has not been well described by such a system, due in part to their
rarity and their variability. Here we present a new system for the
classification of HdCs based on their spectra, which is made wholly on their
observable appearance. We use a combination of dimensionality reduction and
clustering algorithms with human classification to create such a system. We
classify over half of the known sample of HdC stars using this, and roughly
calibrate the temperatures of each class using their colors. Additionally, we
express trends in the occurrence of certain spectral peculiarities such as the
presence of Hydrogen and Lithium lines. We also present three previously
unpublished spectra, and report the discovery of three new Galactic dustless
HdC (dLHdC) stars and additionally discuss one especially unique star that
appears to border between the hottest HdCs and the coolest Extreme Helium (EHe)
stars.Comment: 30 pages, 18 figures, submitted to MNRA
Wide-field dynamic astronomy in the near-infrared with Palomar Gattini-IR and DREAMS
There have been a dramatic increase in the number of optical and radio transient surveys due to astronomical transients such as gravitational waves and gamma ray bursts, however, there have been a limited number of wide-field infrared surveys due to narrow field-of-view and high cost of infrared cameras, we present two new wide-field near-infrared fully automated surveyors; Palomar Gattini-IR and the Dynamic REd All-sky Monitoring Survey (DREAMS). Palomar Gattini-IR, a 25 square degree J-band imager that begun science operations at Palomar Observatory, USA in October 2018; we report on survey strategy as well as telescope and observatory operations and will also providing initial science results. DREAMS is a 3.75 square degree wide-field imager that is planned for Siding Spring Observatory, Australia; we report on the current optical and mechanical design and plans to achieve on-sky results in 2020. DREAMS is on-track to be one of the first astronomical telescopes to use an Indium Galium Arsenide (InGaAs) detector and we report initial on-sky testing results for the selected detector package. DREAMS is also well placed to take advantage and provide near-infrared follow-up of the LSST
The Dynamic Infrared Sky
Opening up the dynamic infrared sky for systematic time-domain exploration
would yield many scientific advances. Multi-messenger pursuits such as
localizing gravitational waves from neutron star mergers and quantifying the
nucleosynthetic yields require the infrared. Another multi-messenger endeavor
that needs infrared surveyors is the study of the much-awaited supernova in our
own Milky Way. Understanding shocks in novae, true rates of supernovae and
stellar mergers are some other examples of stellar evolution and high energy
physics wherein the answers are buried in the infrared. We discuss some of the
challenges in the infrared and pathfinders to overcome them. We conclude with
recommendations on both infrared discovery engines and infrared follow-up
machines that would enable this field to flourish in the next decade.Comment: Astro2020 Science White Paper for Decadal Surve
Constraining the X-ray - Infrared spectral index of second-timescale flares from SGR1935+2154 with Palomar Gattini-IR
The Galactic magnetar SGR1935+2154 has been reported to produce the first
known example of a bright millisecond duration radio burst (FRB 200428) similar
to the cosmological population of fast radio bursts (FRBs), bolstering the
association of FRBs to active magnetars. The detection of a coincident bright
X-ray burst has revealed the first observed multi-wavelength counterpart of a
FRB. However, the search for similar emission at optical wavelengths has been
hampered by the high inferred extinction on the line of sight. Here, we present
results from the first search for second-timescale emission from the source at
near-infrared wavelengths using the Palomar Gattini-IR observing system in
J-band, made possible by a recently implemented detector read-out mode that
allowed for short exposure times of 0.84 s with 99.9% observing efficiency.
With a total observing time of 12 hours (47728 images) on source, we place
median limits on the second-timescale emission of mJy (13.1
AB mag). We present non-detection limits from epochs of four simultaneous X-ray
bursts detected by the Insight-{\it HXMT} and {\it NuSTAR} telescopes during
our observing campaign. The limits translate to an extinction corrected fluence
limit of Jy ms for an estimated extinction of mag. These
limits provide the most stringent constraints to date on the fluence of flares
at frequencies of Hz, and constrain the ratio of the
near-infrared (NIR) fluence to that of coincident X-ray bursts to . Our observations were sensitive enough to easily detect
a near-infrared counterpart of FRB 200428 if the NIR emission falls on the same
power law as that observed across its radio to X-ray spectrum. The
non-detection of NIR emission around the coincident X-ray bursts constrains the
fluence index of the brightest burst to be steeper than .Comment: 10 pages, 4 figures, submitted to ApJL. Comments welcom
Palomar Gattini-IR: Survey overview, data processing system, on-sky performance and first results
Palomar Gattini-IR is a new wide-field, near-infrared (NIR) robotic time domain survey operating at Palomar Observatory. Using a 30 cm telescope mounted with a H2RG detector, Gattini-IR achieves a field of view (FOV) of 25 sq. deg. with a pixel scale of 8.β7 in J-band. Here, we describe the system design, survey operations, data processing system and on-sky performance of Palomar Gattini-IR. As a part of the nominal survey, Gattini-IR scans β7500 square degrees of the sky every night to a median 5Ο depth of 15.7 AB mag outside the Galactic plane. The survey covers β15,000 square degrees of the sky visible from Palomar with a median cadence of 2 days. A real-time data processing system produces stacked science images from dithered raw images taken on sky, together with point-spread function (PSF)-fit source catalogs and transient candidates identified from subtractions within a median delay of β4 hr from the time of observation. The calibrated data products achieve an astrometric accuracy (rms) of β0.β7 with respect to Gaia DR2 for sources with signal-to-noise ratio > 10, and better than β0.β35 for sources brighter than β12 Vega mag. The photometric accuracy (rms) achieved in the PSF-fit source catalogs is better than β3% for sources brighter than β12 Vega mag and fainter than the saturation magnitude of β8.5 Vega mag, as calibrated against the Two Micron All Sky Survey catalog. The detection efficiency of transient candidates injected into the images is better than 90% for sources brighter than the 5Ο limiting magnitude. The photometric recovery precision of injected sources is 3% for sources brighter than 13 mag, and the astrometric recovery rms is β0.β9. Reference images generated by stacking several field visits achieve depths of β³16.5 AB mag over 60% of the sky, while it is limited by confusion in the Galactic plane. With a FOV β40Γ larger than any other existing NIR imaging instrument, Gattini-IR is probing the reddest and dustiest transients in the local universe such as dust obscured supernovae in nearby galaxies, novae behind large columns of extinction within the galaxy, reddened microlensing events in the Galactic plane and variability from cool and dust obscured stars. We present results from transients and variables identified since the start of the commissioning period
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