ABSTRACT
The Weizmann Fast Astronomical Survey Telescope is a 55 cm optical survey telescope with a high-cadence (25 Hz) monitoring of the sky over a wide field of view (≈7 deg2). The high frame rate ...allows detection of sub-second transients over multiple images. We present a sample of ∼0.1–0.3 s duration flares detected in an untargeted survey for such transients. We show that most, if not all of them, are glints of sunlight reflected off geosynchronous and graveyard orbit satellites. The flares we detect have a typical magnitude of 9–11, which translates to ∼14–16th magnitude if diluted by a 30 s exposure time. We estimate the rate of events brighter than ∼11 mag to be of the order of 30–40 events per day per deg2, for declinations between −20° and +10°, not including the declination corresponding to the geostationary belt directly above the equator, where the rate can be higher. We show that such glints are common in large area surveys (e.g. Zwicky Transient Facility and Legacy Survey of Space and Time), and that some of them have a point-like appearance, confounding searches for fast transients such as fast radio burst counterparts and gamma-ray bursts (GRBs). By observing in the direction of the Earth’s shadow, we are able to put an upper limit on the rate of fast astrophysical transients of 0.052 deg−2 day−1 (95 per cent confidence limit) for events brighter than 11 mag. We also suggest that the single image, high declination flare observed in coincidence with the GN-z11 galaxy and assumed to be a GRB, is also consistent with such a satellite glint.
We present the result of calculations to optimize the search for molecular oxygen, O2, in Earth analogs transiting around nearby, low-mass stars using ground-based, high-resolution Doppler shift ...techniques. We investigate a series of parameters, namely spectral resolution, wavelength coverage of the observations, and sky coordinates and systemic velocity of the exoplanetary systems, to find the values that optimize detectability of O2. We find that increasing the spectral resolution of observations to R ∼ 300,000-400,000 from the typical R ∼ 100,000 more than doubles the average depth of O2 lines in planets with atmospheres similar to Earth's. Resolutions higher than ∼500,000 do not produce significant gains in the depths of the O2 lines. We confirm that observations in the O2 A-band are the most efficient except for M9V host stars, for which observations in the O2 near-infrared (NIR) band are more efficient. Combining observations in the O2 A, B, and NIR bands can reduce the number of transits needed to produce a detection of O2 by about one-third in the case of white noise limited observations. However, that advantage disappears in the presence of typical levels of red noise. Therefore, combining observations in more than one band produces no significant gain versus observing only in the A band, unless red noise can be significantly reduced. Blending between the exoplanet's O2 lines and telluric O2 lines is a known problem. We find that problem can be alleviated by increasing the resolution of the observations, and by giving preference to targets near the ecliptic.
A relatively unexplored phase space of transients and stellar variability is that of second and sub-second timescales. We describe a new optical observatory operating in the Negev desert in Israel, ...with a 55 cm aperture, a field of view of 2.°6 נ2.°6 (≈7 deg2) equipped with a high frame rate, low read noise, CMOS camera. The system can observe at a frame rate of up to 90 HZ (full frame), while nominally observations are conducted at 10–25 Hz. The data, generated at a rate of over 6 Gbits s−1 at a frame rate of 25 Hz, are analyzed in real time. The observatory is fully robotic and capable of autonomously collecting data on a few thousand stars in each field each night. We present the system overview, performance metrics, science objectives, and some first results, e.g., the detection of a high rate of glints from geosynchronous satellites, reported in Nir et al. 2020.
We present a novel implementation for extremely high-resolution spectroscopy using custom-designed Fabry-Perot Interferometer (FPI) arrays. For a given telescope aperture at the seeing-limited case, ...these arrays can achieve resolutions well in excess of R ∼ 105 using optical elements that are orders of magnitude smaller in size than standard echelle spectrographs of similar resolution. We apply this method specifically to the search for O2 in exoplanetary atmospheres using the O2 A band at 0.76 m and show how an FPI array composed of ∼10 etalons with parameters optimized for this science case can record R = 3-5 × 105 spectra covering the full O2 A band. Using simulated observations of the atmosphere of a transiting nearby Earth-like planet, we show how observations with an FPI array coupled to a long-slit spectrograph can reduce the number of transit observations needed to produce a 3 detection of O2 by ∼30% compared to observations with an R = 105 echelle spectrograph. This in turn leads to a decrease in an observing program duration of several years. The number of transits needed for a 3 detection can be further reduced by increasing the efficiency of FPI arrays using dualons (an etalon with a buried reflective layer) and by coupling the FPI array to a dedicated spectrograph optimized for the O2 A band.
The supernova (SN) PTF11iqb was initially classified as a Type IIn event caught very early after explosion. It showed narrow Wolf–Rayet (WR) spectral features on day 2 (as in SN 1998S and SN 2013cu), ...but the narrow emission weakened quickly and the spectrum morphed to resemble Types II-L and II-P. At late times, Hα exhibited a complex, multipeaked profile reminiscent of SN 1998S. In terms of spectroscopic evolution, we find that PTF11iqb was a near twin of SN 1998S, although with somewhat weaker interaction with circumstellar material (CSM) at early times, and stronger interaction at late times. We interpret the spectral changes as caused by early interaction with asymmetric CSM that is quickly (by day 20) enveloped by the expanding SN ejecta photosphere, but then revealed again after the end of the plateau when the photosphere recedes. The light curve can be matched with a simple model for CSM interaction (with a mass-loss rate of roughly 10−4 M⊙ yr−1) added to the light curve of a normal SN II-P. The underlying plateau requires a progenitor with an extended hydrogen envelope like a red supergiant at the moment of explosion, consistent with the slow wind speed (<80 km s−1) inferred from narrow Hα emission. The cool supergiant progenitor is significant because PTF11iqb showed WR features in its early spectrum – meaning that the presence of such WR features does not necessarily indicate a WR-like progenitor. Overall, PTF11iqb bridges SNe IIn with weaker pre-SN mass-loss seen in SNe II-L and II-P, implying a continuum between these types.
Owing to their utility for measurements of cosmic acceleration, Type Ia supernovae (SNe Ia) are perhaps the best studied class of SNe, yet the progenitor systems of these explosions largely remain a ...mystery. In the first systematic search for such systems, we have identified 16 SNe Ia-CSM, and here we present new spectra of 13 of them. Six SNe Ia-CSM have been well studied previously, three were previously known but are analyzed in depth for the first time here, and seven are new discoveries from the Palomar Transient Factory. Finally, the host galaxies of SNe Ia-CSM are all late-type spirals similar to the Milky Way, or dwarf irregulars like the Large Magellanic Cloud, which implies that these objects come from a relatively young stellar population. This work represents the most detailed analysis of the SN Ia-CSM class to date.
Abstract
We present the result of calculations to optimize the search for molecular oxygen, O
2
, in Earth analogs transiting around nearby, low-mass stars using ground-based, high-resolution Doppler ...shift techniques. We investigate a series of parameters, namely spectral resolution, wavelength coverage of the observations, and sky coordinates and systemic velocity of the exoplanetary systems, to find the values that optimize detectability of O
2
. We find that increasing the spectral resolution of observations to
R
∼ 300,000–400,000 from the typical
R
∼ 100,000 more than doubles the average depth of O
2
lines in planets with atmospheres similar to Earth’s. Resolutions higher than ∼500,000 do not produce significant gains in the depths of the O
2
lines. We confirm that observations in the O
2
A
-band are the most efficient except for M9V host stars, for which observations in the O
2
near-infrared (NIR) band are more efficient. Combining observations in the O
2
A
,
B
, and NIR bands can reduce the number of transits needed to produce a detection of O
2
by about one-third in the case of white noise limited observations. However, that advantage disappears in the presence of typical levels of red noise. Therefore, combining observations in more than one band produces no significant gain versus observing only in the
A
band, unless red noise can be significantly reduced. Blending between the exoplanet’s O
2
lines and telluric O
2
lines is a known problem. We find that problem can be alleviated by increasing the resolution of the observations, and by giving preference to targets near the ecliptic.
Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock-breakout event. Candidates for such SNe include ...Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a specific relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limits on the shock-breakout velocity. The lower limits on the shock velocity we find are consistent with what is expected for SNe (i.e., ~10 super(4) km s super(-1)). This supports the suggestion that the early-time light curves of SNe IIn are caused by shock breakout in a dense CSM. We note that such a correlation can arise from other physical mechanisms. Performing such a test on other classes of SNe (e.g., superluminous SNe) can be used to rule out the interaction model for a class of events.
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