VLA Observations of the AE Aqr-type Cataclysmic Variable LAMOST J024048.51+195226.9

AE Aqr was until recently the only known magnetic cataclysmic variable (MCV) containing a rapidly spinning (33.08 s) white dwarf (WD). Its radio emission is believed to be a superposition of synchrotron-emitting plasmoids, because it has a positive spectral index spanning three orders of magnitude (≈2–2000 GHz) and is unpolarized. Both characteristics are unusual for MCVs. Recently, Thorstensen has suggested that the cataclysmic variable LAMOST J024048.51+195226.9 (henceforth, J0240+19) is a twin of AE Aqr based on its optical spectra. Optical photometry shows the star to be a high-inclination eclipsing binary with a spin period of 24.93 s, making it the fastest spinning WD. This paper presents three hours of Very Large Array radio observations of J0240+19. These observations show that the persistent radio emission from J0240+19 is dissimilar to that of AE Aqr in that it shows high circular polarization and a negative spectral index. The emission is most similar to that from the nova-like CV V603 Aql. We argue that the radio emission is caused by a superposition of plasmoids emitting plasma radiation or electron cyclotron maser emission from the lower corona of the donor star and not from the magnetosphere near the WD, because the latter site is expected to be modulated at the orbital period of the binary and to show eclipses—of which there is no evidence. The radio source J0240+19, although weak (≲ 1 mJy), is a persistent source in a high-inclination eclipsing binary, making it a good laboratory for studying radio emission from CVs.

First Results on RR Lyrae Stars with the TESS Space Telescope: Untangling the Connections between Mode Content, Colors, and Distances

The Transiting Exoplanet Survey Satellite (TESS) space telescope is collecting continuous, high-precision optical photometry of stars throughout the sky, including thousands of RR Lyrae stars. In this paper, we present results for an initial sample of 118 nearby RR Lyrae stars observed in TESS Sectors 1 and 2. We use differential image photometry to generate light curves and analyze their mode content and modulation properties. We combine accurate light-curve parameters from TESS with parallax and color information from the Gaia mission to create a comprehensive classification scheme. We build a clean sample, preserving RR Lyrae stars with unusual light-curve shapes, while separating other types of pulsating stars. We find that a large fraction of RR Lyrae stars exhibit various low-amplitude modes, but the distribution of those modes is markedly different from those of the bulge stars. This suggests that differences in physical parameters have an observable effect on the excitation of extra modes, potentially offering a way to uncover the origins of these signals. However, mode identification is hindered by uncertainties when identifying the true pulsation frequencies of the extra modes. We compare mode amplitude ratios in classical double-mode stars to stars with extra modes at low amplitudes and find that they separate into two distinct groups. Finally, we find a high percentage of modulated stars among the fundamental mode pulsators, but also find that at least 28% of them do not exhibit modulation, confirming that a significant fraction of stars lack the Blazhko effect.

Swift/XRT Deep Galactic Plane Survey Discovery of a New Intermediate Polar Cataclysmic Variable, Swift J183920.1-045350

We report on the Swift/XRT Deep Galactic Plane Survey discovery and multiwavelength follow-up observations of a new intermediate polar (IP) cataclysmic variable, Swift J183920.1-045350. A 449.7 s spin period is found in XMM-Newton and NuSTAR data, accompanied by a 459.9 s optical period that is most likely the synodic, or beat period, produced from a 5.6 hr orbital period. The orbital period is seen with moderate significance in independent long-baseline optical photometry observations taken with the ZTF and SAAO telescopes. We find that the X-ray pulse fraction of the source decreases with increasing energy. The X-ray spectra are consistent with the presence of an Fe emission line complex with both local and interstellar absorption. In the optical spectra, strong Hα, H i, He i, and He ii emission lines are observed, all common features in magnetic CVs. The source properties are thus typical of known IPs, with the exception of its estimated distance of 2.26 − 0.83 + 1.93 kpc, which is larger than typical, extending the reach of the CV population in our Galaxy.

Optical detection of the rapidly spinning white dwarf in V1460 Her

Accreting magnetic white dwarfs offer an opportunity to understand the interplay between spin-up and spin-down torques in binary systems. Monitoring of the white dwarf spin may reveal whether the white dwarf spin is currently in a state of near-equilibrium, or of uni-directional evolution towards longer or shorter periods, reflecting the recent history of the system and providing constraints for evolutionary models. This makes the monitoring of the spin history of magnetic white dwarfs of high interest. In this paper we report the results of a campaign of follow-up optical photometry to detect and track the 39 sec white dwarf spin pulses recently discovered in Hubble Space Telescope data of the cataclysmic variable V1460 Her. We find the spin pulsations to be present in g-band photometry at a typical amplitude of 0.4 per cent. Under favourable observing conditions, the spin signal is detectable using 2-meter class telescopes. We measured pulse-arrival times for all our observations, which allowed us to derive a precise ephemeris for the white dwarf spin. We have also derived an orbital modulation correction that can be applied to the measurements. With our limited baseline of just over four years, we detect no evidence yet for spin-up or spin-down of the white dwarf, obtaining a lower limit of $|P/\dot{P}| > 4\times 10^{7}$ years, which is already 4 to 8 times longer than the timescales measured in two other cataclysmic variable systems containing rapidly rotating white dwarfs, AE Aqr and AR Sco.

Searching for exoplanets around M-dwarfs with ExTrA

<p>ExTrA (Exoplanets in Transits and their Atmospheres - Bonfils et al. 2015) is a new instrument composed of an array of three 60-cm telescopes capable of infrared photometry and located in La Silla, Chile. This instrument relies on a new approach that involves combining optical photometry with spectroscopic information in order to mitigate the disruptive effect of Earth’s atmosphere, as well as effects introduced by instruments and detectors.  ExTrA is currently being used to confirm TESS planet detections around M-dwarfs, refine transit parameters, and search for additional exoplanets in the same systems. ExTrA obtains a better precision for the planetary radius and for the transit timings for late M-type stars with one or a few TESS transits. This work already led to the confirmation of a mini-Neptune around the M-dwarf TOI-269 (Cointepas et al. 2021). ExTrA will also work in tandem with NIRPS, a near-infrared spectrograph that will join HARPS (High Accuracy Radial velocity Planet Searcher) on the 3.6m ESO telescope to conduct a comprehensive radial-velocity survey on M dwarfs. </p>

Study of UV-bright stellar populations in the globular cluster NGC 1261 using Astrosat

ABSTRACT We present UV photometry of the globular cluster NGC 1261 using images acquired with the Ultraviolet Imaging Telescope (UVIT) on board Astrosat. We performed point-spread function (PSF) photometry on four near-UV (NUV) and two far-UV (FUV) images and constructed UV colour–magnitude diagrams (CMDs), in combination with the Hubble Space Telescope (HST), Gaia, and ground-based optical photometry for member stars. We detected the full horizontal branch (HB) in the NUV and blue HB in the FUV and identified two extreme HB (EHB) stars. HB stars have a tight sequence in UV–optical CMDs, well fitted with isochrones generated (age 12.6 Gyr, [Fe/H] = −1.27 metallicity) using updated BaSTI-IAC models. Effective temperatures (Teff), luminosities, and radii of bright HB stars were estimated using the spectral energy distribution. As we detect the complete sample of UV-bright HB stars, the hot end of the HB distribution is found to terminate at the G-jump ($T_{\rm eff}\, \sim$ 11500 K). The two EHB stars, fitted well with single spectra, have Teff = 31000 K and a mass = 0.495 M⊙, and follow the same Teff–radius relation as the blue HB stars. We constrain the formation pathways of these EHB stars to extreme mass loss in the RGB phase (due either to rotation or enhanced helium) or a early hot-flash scenario.

Galactic cirri in deep optical imaging

The ubiquitous presence of Galactic cirri in deep optical images represents a major obstacle to study the low surface brightness features of extragalactic sources. To address this issue, we have explored the optical properties of cirri using g, r, i, and z bands in the Sloan Digital Sky Survey (SDSS) Stripe82 region. Using state-of-the-art, custom made, image processing techniques, including the modeling and removal of the instrumental scattered light produced by the stars, we managed to isolate the optical diffuse emission by the cirri, allowing their photometric characterization. We find that their optical colors are driven by the dust column density: The cirri become redder as their 100 μm emission increases. Remarkably, the optical colors of the Galactic cirri differ significantly from those of extragalactic sources, with a characteristic bluer r-i color for a given g-r, allowing one to detect these by using a simple color relation. Our results show the high potential of deep multi-band optical photometry, on its own, identifying the presence of cirri at a higher spatial resolution than those provided by far-infrared observations. The combination of very deep data and multi-band photometry (as the one produced by LSST and Euclid) would make it possible to build dust maps of unprecedented quality.

Discovery of a new extreme changing-state quasar with 4 mag variation, SDSS J125809.31+351943.0

We report the discovery of a quasar, SDSS J125809.31+351943.0 (J1258), which brightened in optical wavelengths for 4 mag from 1983 to 2015: one of the largest quasar brightening events so far. The history of optical photometry data of this quasar from the Catalina Real-time Transient Survey and All Sky Automated Survey for Super Novae (ASAS-SN), mid-infrared photometry data from the WISE satellite, and the broad emission line (BEL) flux obtained by spectroscopy of the Sloan Digital Sky Survey shows significant increases between 2003 and 2015. Investigating the Canada–France–Hawaii Telescope photometric observations in 1983 and the United States Naval Observatory B catalogue, which contains data from 1975 and 1969, we found that the source was 4 mag fainter before than at the peak of the recent ASAS-SN photometry. From the history of these data, we identified J1258 as a new changing-state quasar (CSQ). We also performed follow-up spectroscopic observations in 2018 December and 2019 May using the 2 m telescope at the Nishi-Harima Astronomical Observatory. The results show that the continuum flux and the BEL flux decreased to about 50% of their peak. This indicates that J1258 present two changing states for the BEL flux and continuum flux. We argue that J1258’s variability, especially its brightening event, can be explained by the propagation of the heating front and the accretion disk state transitions based on the timescale and Eddington ratio variations. The estimated mass of the black hole of J1258 is about an order of magnitude larger than the CSQs found so far. Since both the changing timescale and the size of the accretion disk depend on the black hole mass, the J1258 brightening event can be interpreted as a scaled version of the variability in other CSQs. This suggests that samples of distant quasars with larger black hole masses may contain objects with longer and more severe variations.

138175 (2000 EE104) and the Source of Interplanetary Field Enhancements

<p>We present the first optical observations taken to characterize the near-Earth object 138175 (2000 EE104).  This body is associated with Interplanetary Field Enhancements (IFEs), thought to be caused by interactions between the solar wind magnetic field and solid material trailing in the orbit of the parent body.  Based on optical photometry, the radius (in meters) and mass (in kilograms) of an equal-area sphere are found to be  250(0.1/p)^{1/2} and  1e11(0.1/p)^{3/2}, respectively, where p is the red geometric albedo and density 1500 kg/m3 is assumed.  The measured colors are intermediate between those of C-type (primitive) and S-type (metamorphosed) asteroids but, with correction for the likely effects of phase-reddening, are more consistent with a C-type classification than with S-type. No evidence for co-moving companions larger than 40(0.1/p) meter in radius is found, and no dust particle trail is detected, setting a limit to the trail optical depth < 2e-9.  Consideration of the size distribution  produced by impact pulverization  makes it difficult to generate the  mass of nanodust (minimum 1e5 kg to 1e6 kg) required to account for IFEs, unless the size distribution is unusually steep.  While the new optical data do not definitively refute the hypothesis that boulder pulverization is the source of IFEs, neither do they provide any support for it.</p> <p>Journal: Planetary Science Journal, submitted</p>