Search Publications
Solar-metallicity gas in the extended halo of a galaxy at z ∼ 0.12
Pradeep, Jayadev; Narayanan, Anand; Khaire, Vikram +4 more
We present the detection and analysis of a weak low-ionization absorber at z = 0.121 22 along the sightline of the blazar PG 1424+240, using spectroscopic data from both HST/COS and STIS. The absorber is a weak Mg II analogue, with an incidence of weak C II and Si II, along with multicomponent C IV and O VI. The low ions are tracing a dense (n
Magnetic Flux Emergence in a Coronal Hole
Denker, Carsten; Temmer, Manuela; Veronig, Astrid +13 more
A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (Hinode Observing Plan 338, 20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum Tower Telescope (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole r…
Electromagnetic counterparts to gravitational wave events from Gaia
Harrison, D. L.; Koposov, S. E.; Evans, D. W. +15 more
The recent discoveries of gravitational wave events and in one case also its electromagnetic (EM) counterpart allow us to study the Universe in a novel way. The increased sensitivity of the LIGO and Virgo detectors has opened the possibility for regular detections of EM transient events from mergers of stellar remnants. Gravitational wave sources …
A comparative analysis of denoising algorithms for extragalactic imaging surveys
Castellano, M.; Merlin, E.; Fontana, A. +4 more
Aims: We present a comprehensive analysis of the performance of noise-reduction (denoising) algorithms to determine whether they provide advantages in source detection, mitigating noise on extragalactic survey images.
Methods: The methods we analyze here are representative of different algorithmic families: Perona-Malik filtering, bilate…
Characterizing continuum variability in the radio-loud narrow-line Seyfert 1 galaxy IRAS 17020+4544
Fabian, A. C.; Gallo, L. C.; Alston, W. N. +4 more
We present results of temporal and spectral analyses on four XMM-Newton EPIC pn observations of IRAS 17020+4544, a narrow-line Seyfert 1 galaxy with evidence of a radio jet. Analysis of the light curves reveals that this radio-loud source does not behave like the bulk population of its radio-quiet counterparts. A trend of spectral hardening with i…
Shape model and spin state of non-principal axis rotator (5247) Krylov
Duffard, R.; Marciniak, A.; Ďurech, J. +12 more
Context. The study of non-principal axis (NPA) rotators can provide important clues to the evolution of the spin state of asteroids. However, very few studies to date have focused on NPA-rotating main belt asteroids (MBAs). One MBA known to be in an excited rotation state is asteroid (5247) Krylov.
Aims: By using disk-integrated photometric d…
Multiwavelength classification of X-ray selected galaxy cluster candidates using convolutional neural networks
Kendrew, Sarah; Valtchanov, Ivan; Werner, Norbert +15 more
Galaxy clusters appear as extended sources in XMM-Newton images, but not all extended sources are clusters. So, their proper classification requires visual inspection with optical images, which is a slow process with biases that are almost impossible to model. We tackle this problem with a novel approach, using convolutional neural networks (CNNs)…
Fundamental parameters of Ap-star HD 108662
Romanovskaya, A. M.; Ryabchikova, T. A.; Shulyak, D. V.
We present the results of self-consistent spectroscopic analysis of the atmosphere of Ap-star HD 108662 based on high resolution spectrum and spectrophotometric observations in a wide wavelength range. Magnetic field effects were taking into account. Abundances of 24 chemical elements were derived, and stratification of Fe which lines make the mai…
HD 93795: a late-B supergiant star with a square circumstellar nebula
Katkov, I. Y.; Gvaramadze, V. V.; Castro, N. +1 more
We report the discovery of a square axisymmetric circumstellar nebula around the emission-line star HD 93795 in the archival Spitzer Space Telescope 24 {µ m} data. We classify HD 93795 as a B9 Ia star using optical spectra obtained with the Southern African Large Telescope (SALT). A spectral analysis carried out with the stellar atmosphere c…
Investigation of the coronal heating through phase relation of solar activity indexes
Li, K. J.; Xu, J. C.; Yin, Z. Q. +2 more
The coronal heating problem is a long-standing perplexing issue. In this study, 13 solar activity indexes are used to investigate their phase relation with the sunspot number (SSN). Only three of them are found to statistically significantly lag the SSN (large-scale magnetic activity) by about one solar rotation period; the three indexes are total…