Extended gas clouds have been previously detected surrounding the brightest known close-in transiting hot Jupiter exoplanets, HD 209458 b and HD 189733 b; we observed the distant but more extreme ...close-in hot Jupiter system, WASP-12, with Hubble Space Telescope (HST). Near-UV (NUV) transits up to three times deeper than the optical transit of WASP-12 b reveal extensive diffuse gas, extending well beyond the Roche lobe. Our spectra reveal significantly enhanced absorption (greater than 3sigma below the median) at ~200 individual wavelengths on each of two HST visits; 65 of these wavelengths are consistent between the two visits, using a strict criterion for velocity matching that excludes matches with velocity shifts exceeding ~20 km s super(-1). Our Visit 2 NUV light curves show evidence for a stellar flare. We show that some of the possible transit detections in resonance lines of rare elements may be due instead to non-resonant transitions in common species. We present optical observations and update the transit ephemeris.
ABSTRACT
Our nearest stellar neighbour, Proxima Centauri, is a low-mass star with spectral type dM5.5 and hosting an Earth-like planet orbiting within its habitable zone. However, the habitability of ...the planet depends on the high-energy radiation of the chromospheric and coronal activity of the host star. We report the AstroSat, Chandra, and HST observation of Proxima Centauri carried out as part of the multiwavelength simultaneous observational campaign. Using the soft X-ray data, we probe the different activity states of the star. We investigate the coronal temperatures, emission measures and abundance. Finally, we compare our results with earlier observations of Proxima Centauri.
Context.
The space density of X-ray-luminous, blindly selected active galactic nuclei (AGN) traces the population of rapidly accreting super-massive black holes through cosmic time. It is encoded in ...the X-ray luminosity function, whose bright end remains poorly constrained in the first billion years after the Big Bang as X-ray surveys have thus far lacked the required cosmological volume. With the eROSITA Final Equatorial-Depth Survey (eFEDS), the largest contiguous and homogeneous X-ray survey to date, X-ray AGN population studies can now be extended to new regions of the luminosity–redshift space (
L
2 − 10 keV
> 10
45
erg s
−1
and
z
> 6).
Aims.
The current study aims at identifying luminous quasars at
z
> 5.7 among X-ray-selected sources in the eFEDS field in order to place a lower limit on black hole accretion well into the epoch of re-ionisation. A secondary goal is the characterisation of the physical properties of these extreme coronal emitters at high redshifts.
Methods.
Cross-matching eFEDS catalogue sources to optical counterparts from the DESI Legacy Imaging Surveys, we confirm the low significance detection with eROSITA of a previously known, optically faint
z
= 6.56 quasar from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed follow-up observation of the source with the
Chandra
X-ray telescope in order to confirm the low-significance eROSITA detection. Using new near-infrared spectroscopy, we derived the physical properties of the super-massive black hole. Finally, we used this detection to infer a lower limit on the black hole accretion density rate at
z
> 6.
Results.
The
Chandra
observation confirms the eFEDS source as the most distant blind X-ray detection to date. The derived X-ray luminosity is high with respect to the rest-frame optical emission of the quasar. With a narrow Mg
II
line, low derived black hole mass, and high Eddington ratio, as well as its steep photon index, the source shows properties that are similar to local narrow-line Seyfert 1 galaxies, which are thought to be powered by young super-massive black holes. In combination with a previous high-redshift quasar detection in the field, we show that quasars with
L
2 − 10 keV
> 10
45
erg s
−1
dominate accretion onto super-massive black holes at
z
∼ 6.
The HU Aqr planetary system hypothesis revisited Goździewski, K; Słowikowska, A; Dimitrov, D ...
Monthly notices of the Royal Astronomical Society,
04/2015, Letnik:
448, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We study the mid-egress eclipse timing data gathered for the cataclysmic binary HU Aquarii during the years 1993–2014. The (O−C) residuals were previously attributed to a single ∼7 Jupiter mass ...companion in ∼5 au orbit or to a stable two-planet system with an unconstrained outermost orbit. We present 22 new observations gathered between 2011 June and 2014 July with four instruments around the world. They reveal a systematic deviation of ∼60–120 s from the older ephemeris. We re-analyse the whole set of the timing data available. Our results provide an erratum to the previous HU Aqr planetary models, indicating that the hypothesis for a third and fourth body in this system is uncertain. The dynamical stability criterion and a particular geometry of orbits rule out coplanar two-planet configurations. A putative HU Aqr planetary system may be more complex, e.g. highly non-coplanar. Indeed, we found examples of three-planet configurations with the middle planet in a retrograde orbit, which are stable for at least 1 Gyr, and consistent with the observations. The (O−C) may be also driven by oscillations of the gravitational quadrupole moment of the secondary, as predicted by the Lanza et al. modification of the Applegate mechanism. Further systematic, long-term monitoring of HU Aqr is required to interpret the (O−C) residuals.
We present a simple heuristic model for the time-averaged soft X-ray temperature distribution in the accretion spot on the white dwarf in polars. The model is based on the analysis of the Chandra ...LETG spectrum of the prototype polar AM Her and involves an exponential distribution of the emitting area vs. blackbody temperature a(T) = a0 exp( − T/T0). With one free parameter besides the normalization, it is mathematically as simple as the single blackbody, but is physically more plausible and fits the soft X-ray and far-ultraviolet spectral fluxes much better. The model yields more reliable values of the wavelength-integrated flux of the soft X-ray component and the implied accretion rate than reported previously.
The Microchannel X-ray Telescope (MXT) will be the first focusing X-ray telescope based on a narrow field “Lobster-Eye” optical design to be flown on a satellite, namely the Sino-French mission SVOM. ...SVOM will be dedicated to the study of Gamma-Ray Bursts and more generally time-domain astrophysics. The MXT telescope is a compact (focal length
∼
1.15 m) and light (< 42 kg) instrument, sensitive in the 0.2–10 keV energy range. It is composed of an optical system, based on micro-pore optics (MPOs) of 40
μ
m pore size, coupled to a low-noise pnCDD X-ray detector. In this paper we describe the expected scientific performance of the MXT telescope, based on the End-to-End calibration campaign performed in fall 2021, before the integration of the SVOM payload on the satellite.
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