Astronomische Nachrichten

Journal Information
ISSN / EISSN : 0004-6337 / 1521-3994
Published by: Wiley-Blackwell (10.1002)
Total articles ≅ 48,214
Current Coverage
SCOPUS
SCIE
Archived in
EBSCO
SHERPA/ROMEO
Filter:

Latest articles in this journal

, Surajit Paul, Gopal Krishna
Published: 21 October 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.20210038

Abstract:
We report our ongoing search for extremely inverted spectrum compact radio galaxies, for which the defining feature in the radio spectrum is not the spectral peak, but instead the slope of the spectrum () in the high-opacity (i.e., lower frequency) part of the radio spectrum. Specifically, our focus is on the spectral regime with a spectral index, . The motivation for our study is, first, extragalactic sources with such extreme spectral index are extremely rare, because of the unavailability of the right combination of sensitivity and resolution over a range of low frequencies. The second reason is more physically motivated since α = +2.5 is the maximum slope theoretically possible for a standard radio source emitting synchrotron radiation. Therefore such sources could be the test-bed for some already proposed alternative scenarios for synchrotron self-absorption (SSA), like the free-free absorption (FFA) highlighting the importance of jet-ISM interaction in the radio galaxy evolution.
, Leonardo Di Venere, Giulia Migliori, Monica Orienti, Filippo D'Ammando, the Fermi‐LAT Collaboration
Published: 20 October 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.20210041

Abstract:
According to radiative models, radio galaxies are predicted to produce γ-rays from the earliest stages of their evolution onwards. The study of the high-energy emission from young radio sources is crucial for providing information on the most energetic processes associated with these sources, the actual region responsible for this emission, as well as the structure of the newly born radio jets. Despite systematic searches for young radio sources at γ-ray energies, only a handful of detections have been reported so far. Taking advantage of more than 11 years of Fermi-large area telescope (LAT) data, we investigate the γ-ray emission of 162 young radio sources (103 galaxies and 59 quasars), the largest sample of young radio sources used so far for a γ-ray study. We analyzed the Fermi-LAT data of each source separately to search for a significant detection. In addition, we performed the first stacking analysis of this class of sources in order to investigate the γ-ray emission of the young radio sources that are undetected at high energies. In this note, we present the results of our study and we discuss their implications for the predictions of γ-ray emission from this class of sources.
, Magdalena Kunert‐Bajraszewska, Aneta Siemiginowska, Douglas J. Burke, Françoise Combes, Philippe Salomé, Simona Giacintucci
Published: 20 October 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.20210035

The publisher has not yet granted permission to display this abstract.
, , Richard L. Branham Jr, Amnah S. Al‐Johani
Published: 14 October 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.20210019

The publisher has not yet granted permission to display this abstract.
Radoslav K. Zamanov, , Andon Kostov, Alexander Kurtenkov, Grigor Nikolov, Georgi Latev, Michael F. Bode, Josep Martí, Pedro L. Luque‐Escamilla, Nikolay Tomov, et al.
Published: 23 September 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.202113975

The publisher has not yet granted permission to display this abstract.
, Markus Mugrauer, Guillermo Torres, Michael Geymeier, Ralph Neuhäuser, Wolfgang Stenglein, Kai‐Uwe Michel
Published: 20 September 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.202113962

Abstract:
Runaway stars are characterized by their remarkably high space velocities, and the study of their formation mechanisms has attracted considerable interest. Young, nearby runaway stars are the most favorable for identifying their place of origin, and for searching for possible associated objects such as neutron stars. Usually, the research field of runaway stars focuses on O- and B-type stars, because these objects are better detectable at larger distances than late-type stars. Early-type runaway stars have the advantage that they evolve faster and can therefore better be confirmed to be young. In contrast to this, the catalog of Young runaway stars within 3 kpc by Tetzlaff, N., Neuhäuser, R., & Hohle, M. M. (2011, MNRAS, 410(1), 190–200) contains also stars of spectral type A and later. The objects in this catalog were originally classified as young ( Myr) runaway stars by using Hipparcos data to estimate the ages from their location in the Hertzsprung-Russell diagram and evolutionary models. In this article, we redetermine and/or constrain their ages not only by using the more precise second data release of the Gaia mission, but also by measuring the equivalent width of the lithium (6,708 Å) line, which is a youth indicator. Therefore, we searched for lithium absorption in the spectra of 51 target stars, taken at the University Observatory Jena between March and September 2020 with the Échelle spectrograph FLECHAS, and within additional TRES-spectra from the Fred L. Whipple Observatory. The main part of this campaign with its 308 reduced spectra, accessible at VizieR, was already published. In this work, which is the continuation and completion of the in 2015 initiated observing campaign, we found three additional young runaway star candidates.
, Orhan Güneş, Yüksel Karataş, Charles Bonatto
Published: 12 September 2021
Astronomische Nachrichten; https://doi.org/10.1002/asna.202113983

The publisher has not yet granted permission to display this abstract.
Back to Top Top