We present the first X-ray spectrum obtained by the Low-Energy Transmission Grating Spectrometer (LETGS) aboard the Chandra X-Ray Observatory. The spectrum is of Capella and covers a wavelength range ...of 5-175 Å (2.5-0.07 keV). The measured wavelength resolution, which is in good agreement with ground calibration, is Deltalambda approximately 0.06 Å (FWHM). Although in-flight calibration of the LETGS is in progress, the high spectral resolution and unique wavelength coverage of the LETGS are well demonstrated by the results from Capella, a coronal source rich in spectral emission lines. While the primary purpose of this Letter is to demonstrate the spectroscopic potential of the LETGS, we also briefly present some preliminary astrophysical results. We discuss plasma parameters derived from line ratios in narrow spectral bands, such as the electron density diagnostics of the He-like triplets of carbon, nitrogen, and oxygen, as well as resonance scattering of the strong Fe xvii line at 15.014 Å.
We used the large binocular camera (LBC) mounted on the large binocular telescope (LBT) to observe the Lockman Hole in the U, B, and V bands. Our observations cover an area of 925 arcmin2. We reached ...depths of 26.7, 26.3, and 26.3 mag(AB) in the three bands, respectively, in terms of 50% source detection efficiency, making this survey the deepest U-band survey and one of the deepest B and V band surveys with respect to its covered area. We extracted a large number of sources (~89 000), detected in all three bands and examined their surface density, comparing it with models of galaxy evolution. We find good agreement with previous claims of a steep faint-end slope of the luminosity functions, caused by late-type and irregular galaxies at $z>1.5$. A population of dwarf star-forming galaxies at $1.5<z<2.5$ is needed to explain the U-band number counts. We also find evidence of strong supernova feedback at high redshift. This survey is complementary to the r, i, and z Lockman Hole survey conducted with the Subaru telescope and provides the essential wavelength coverage to derive photometric redshifts and select different types of sources from the Lockman Hole for further study.
We introduce PIRATE, a new remotely operable telescope facility for use in research and education, constructed from off-the-shelf hardware, operated by The Open University. We focus on the PIRATE ...Mark 1 operational phase, in which PIRATE was equipped with a widely used 0.35 m Schmidt-Cassegrain system (now replaced with a 0.425 m corrected Dall-Kirkham astrograph). Situated at the Observatori Astronòmic de Mallorca, PIRATE is currently used to follow up potential transiting extrasolar planet candidates produced by the SuperWASP North experiment, as well as to hunt for novae in M31 and other nearby galaxies. It is operated by a mixture of commercially available software and proprietary software developed at the Open University. We discuss problems associated with performing precision time-series photometry when using a German Equatorial Mount, investigating the overall performance of such off-the-shelf solutions in both research and teaching applications. We conclude that PIRATE is a cost-effective research facility, and it also provides exciting prospects for undergraduate astronomy. PIRATE has broken new ground in offering practical astronomy education to distance-learning students in their own homes.
The high-energy environments of host stars could prove deleterious for their planets. It is crucial to ascertain this contextual information to characterize the atmospheres of terrestrial exoplanets. ...We aim to fully characterize a unique triple system, LTT1445, with three known rocky planets around LTT 1445A. We studied the X-ray irradiation and flaring of this system based on a new 50 ks Chandra observation, which is divided into 10 ks, 10 ks, and 30 ks segments conducted two days apart, and two months apart, respectively. These data were complemented by an archival Chandra observation approximately one year earlier and repeated observations with extended ROentgen Survey with an Imaging Telescope Array (eROSITA), the soft X-ray instrument on the Spectrum-Roentgen-Gamma (SRG) mission. This enabled the investigation of X-ray flux behavior across multiple time scales. With the observed X-ray flux from the exoplanet host star A, we estimated the photo-evaporation mass loss of each exoplanet. With the planet modeling package VPLanet we predicted the evolution and anticipated current atmospheric conditions. Our Chandra observations indicate that LTT 1445C is the dominant X-ray source, with additional contribution from LTT 1445B. We find that LTT 1445A, a slowly rotating star, exhibits no significant flare activity in the new Chandra dataset. Comparing the flux incident occuring on the exoplanets, we find that LTT 1445BC components do not pose a greater threat to the planets orbiting LTT 1445A than the emission from A itself. According to the results from the simulation, LTT 1445Ad could have the capacity to retain its water surface.
Neglected X-ray discovered polars Beuermann, K.; Burwitz, V.; Reinsch, K. ...
Astronomy and astrophysics (Berlin),
02/2020, Letnik:
634
Journal Article
Recenzirano
Odprti dostop
We report on the X-ray observations of the eclipsing polar HY Eri (RX J0501–0359), along with its photometric, spectrophotometric, and spectropolarimetric optical variations, collected over 30 years. ...With an orbital period of 2.855 h,
HY Eri
falls near the upper edge of the 2–3 h period gap. After 2011, the system went into a prolonged low state, continuing to accrete at a low level. We present an accurate alias-free long-term orbital ephemeris and report a highly significant period change by 10 ms that took place over the time interval from 2011 to 2018. We acquired a high-quality eclipse spectrum that shows the secondary star as a dM5–6 dwarf at a distance
d
= 1050 ± 110 pc. Based on phase-resolved cyclotron and Zeeman spectroscopy, we identify the white dwarf (WD) in
HY Eri
as a two-pole accretor with nearly opposite accretion spots of 28 and 30 MG. The Zeeman analysis of the low state spectrum reveals a complex magnetic field structure, which we fit by a multipole model. We detected narrow emission lines from the irradiated face of the secondary star, of which Mg I
λ
5170 with a radial velocity amplitude of
K
′
2
= 139 ± 10 km s
−1
(90% confidence) tracks the secondary more reliably than the narrow H
α
line. Based on the combined dynamical analysis and spectroscopic measurement of the angular radius of the WD, we obtain a primary mass of
M
1
= 0.42 ± 0.05
M
⊙
(90% confidence errors), identifying it as a probable He WD or hybrid HeCO WD. The secondary is a main sequence star of
M
2
= 0.24 ± 0.04
M
⊙
that seems to be slightly inflated. The large distance of
HY Eri
and the lack of similar systems suggest a very low space density of polars with low-mass primary. According to current theory, these systems are destroyed by induced runaway mass transfer, suggesting that
HY Eri
may be doomed to destruction. Over the last 30 years,
HY Eri
experienced high and low states with mass transfer rates that differed by three orders of magnitude, varying between
Ṁ
≃ 10
−9
M
⊙
yr
−1
and 10
−12
M
⊙
yr
−1
. At a galactic latitude of −26.1°, it is located about 500 pc below the galactic plane.
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