26 research outputs found
A search for rapidly pulsating hot subdwarf stars in the GALEX survey
NASA's Galaxy Evolution Explorer (GALEX) provided near- and far-UV
observations for approximately 77 percent of the sky over a ten-year period;
however, the data reduction pipeline initially only released single NUV and FUV
images to the community. The recently released Python module gPhoton changes
this, allowing calibrated time-series aperture photometry to be extracted
easily from the raw GALEX data set. Here we use gPhoton to generate light
curves for all hot subdwarf B (sdB) stars that were observed by GALEX, with the
intention of identifying short-period, p-mode pulsations. We find that the
spacecraft's short visit durations, uneven gaps between visits, and dither
pattern make the detection of hot subdwarf pulsations difficult. Nonetheless,
we detect UV variations in four previously known pulsating targets and report
their UV pulsation amplitudes and frequencies. Additionally, we find that
several other sdB targets not previously known to vary show promising signals
in their periodograms. Using optical follow-up photometry with the Skynet
Robotic Telescope Network, we confirm p-mode pulsations in one of these
targets, LAMOST J082517.99+113106.3, and report it as the most recent addition
to the sdBVr class of variable stars.Comment: 11 Pages, 8 Figures, Accepted for publication in the Astrophysical
Journa
Orbital Foregrounds for Ultra-Short Duration Transients
Reflections from objects in Earth orbit can produce sub-second, star-like
optical flashes similar to astrophysical transients. Reflections have
historically caused false alarms for transient surveys, but the population has
not been systematically studied. We report event rates for these orbital
flashes using the Evryscope Fast Transient Engine, a low-latency transient
detection pipeline for the Evryscopes. We select single-epoch detections likely
caused by Earth satellites and model the event rate as a function of both
magnitude and sky position. We measure a rate of
sky hour, peaking at , for flashes morphologically
degenerate with real astrophysical signals in surveys like the Evryscopes. Of
these, sky hour are bright enough to be
visible to the naked eye in typical suburban skies with a visual limiting
magnitude of . These measurements place the event rate of orbital
flashes orders of magnitude higher than the combined rate of public alerts from
all active all-sky fast-timescale transient searches, including neutrino,
gravitational-wave, gamma-ray, and radio observatories. Short-timescale orbital
flashes form a dominating foreground for un-triggered searches for fast
transients in low-resolution, wide-angle surveys. However, events like fast
radio bursts (FRBs) with arcminute-scale localization have a low probability
() of coincidence with an orbital flash, allowing optical surveys
to place constraints on their potential optical counterparts in single images.
Upcoming satellite internet constellations, like SpaceX Starlink, are unlikely
to contribute significantly to the population of orbital flashes in normal
operations.Comment: 8 pages, 4 figure
EvryFlare. III. Temperature Evolution and Habitability Impacts of Dozens of Superflares Observed Simultaneously by Evryscope and TESS
Superflares may provide the dominant source of biologically relevant UV radiation to rocky habitable-zone M-dwarf planets (M-Earths), altering planetary atmospheres and conditions for surface life. The combined line and continuum flare emission has usually been approximated by a 9000 K blackbody. If superflares are hotter, then the UV emission may be 10 times higher than predicted from the optical. However, it is unknown for how long M-dwarf superflares reach temperatures above 9000 K. Only a handful of M-dwarf superflares have been recorded with multiwavelength high-cadence observations. We double the total number of events in the literature using simultaneous Evryscope and Transiting Exoplanet Survey Satellite observations to provide the first systematic exploration of the temperature evolution of M-dwarf superflares. We also increase the number of superflaring M dwarfs with published time-resolved blackbody evolution by ∼10×. We measure temperatures at 2 minutes cadence for 42 superflares from 27 K5–M5 dwarfs. We find superflare peak temperatures (defined as the mean of temperatures corresponding to flare FWHM) increase with flare energy and impulse. We find the amount of time flares emit at temperatures above 14,000 K depends on energy. We discover that 43% of the flares emit above 14,000 K, 23% emit above 20,000 K and 5% emit above 30,000 K. The largest and hottest flare briefly reached 42,000 K. Some do not reach 14,000 K. During superflares, we estimate M-Earths orbiting <200 Myr stars typically receive a top-of-atmosphere UV-C flux of ∼120 W m−2 and up to 103 W m−2, 100–1000 times the time-averaged X-ray and UV flux from Proxima Cen
Long-term thermal sensitivity of Earth’s tropical forests
The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate