A Search for Radio Emission at the Bottom of the Main Sequence and Beyond

1999 ◽  
Vol 118 (3) ◽  
pp. 1369-1372 ◽  
Author(s):  
Anita Krishnamurthi ◽  
Giuseppe Leto ◽  
Jeffrey L. Linsky
Keyword(s):  
Radio Emission ◽  
Main Sequence

scholarly journals HST/STIS analysis of the first main sequence pulsar CU Virginis

2019 ◽  
Vol 625 ◽  
pp. A34 ◽  
Author(s):  
J. Krtička ◽  
Z. Mikulášek ◽  
G. W. Henry ◽  
J. Janík ◽  
O. Kochukhov ◽  
...  
Keyword(s):  
Radio Emission ◽  
Main Sequence ◽  
Flux Distribution ◽  
Mass Loss Rate ◽  
Rotational Period ◽  
Uv Spectrum ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
Chemically Peculiar Stars

Context. CU Vir has been the first main sequence star that showed regular radio pulses that persist for decades, resembling the radio lighthouse of pulsars and interpreted as auroral radio emission similar to that found in planets. The star belongs to a rare group of magnetic chemically peculiar stars with variable rotational period. Aims. We study the ultraviolet (UV) spectrum of CU Vir obtained using STIS spectrograph onboard the Hubble Space Telescope (HST) to search for the source of radio emission and to test the model of the rotational period evolution. Methods. We used our own far-UV and visual photometric observations supplemented with the archival data to improve the parameters of the quasisinusoidal long-term variations of the rotational period. We predict the flux variations of CU Vir from surface abundance maps and compare these variations with UV flux distribution. We searched for wind, auroral, and interstellar lines in the spectra. Results. The UV and visual light curves display the same long-term period variations supporting their common origin. New updated abundance maps provide better agreement with the observed flux distribution. The upper limit of the wind mass-loss rate is about 10−12 M⊙ yr−1. We do not find any auroral lines. We find rotationally modulated variability of interstellar lines, which is most likely of instrumental origin. Conclusions. Our analysis supports the flux redistribution from far-UV to near-UV and visual domains originating in surface abundance spots as the main cause of the flux variability in chemically peculiar stars. Therefore, UV and optical variations are related and the structures leading to these variations are rigidly confined to the stellar surface. The radio emission of CU Vir is most likely powered by a very weak presumably purely metallic wind, which leaves no imprint in spectra.

scholarly journals Radio Emission from Binary Stars in the AB Doradus Moving Group

2015 ◽  
Vol 10 (S314) ◽  
pp. 117-118
Author(s):  
R. Azulay ◽  
J.C. Guirado ◽  
J.M. Marcaide ◽  
I. Martí-Vidal ◽  
E. Ros
Keyword(s):  
Radio Emission ◽  
Binary Stars ◽  
Binary Systems ◽  
Main Sequence ◽  
Precise Determination ◽  
Orbital Parameters ◽  
Long Baseline ◽  
Low Mass ◽  
The Individual ◽  
Dynamical Masses

AbstractPrecise determination of dynamical masses of pre-main-sequence stars is essential for calibrating stellar evolution models, that are widely used to derive theoretical masses of young low-mass objects. We have determined the individual masses of the pair AB Dor Ba/Bb using Australian Long Baseline Array observations and archive infrared data, as part of a larger program directed to monitor binary systems in the AB Doradus moving group. We have detected, for the first time, compact radio emission from both stars. This has allowed us to determine the orbital parameters of both the relative and absolute orbits and, consequently, their individual dynamical masses: 0.28±0.05 M⊙ and 0.25±0.05 M⊙. Comparisons of the dynamical masses with the prediction of pre-main-sequence (PMS) evolutionary models show that the models underpredict the dynamical masses of the binary components Ba and Bb by 10–30% and 10–40%, respectively.

scholarly journals Optical spectral properties of radio loud quasars along the main sequence

2019 ◽  
Vol 15 (S356) ◽  
pp. 310-313
Author(s):  
Ascensión del Olmo ◽  
Paola Marziani ◽  
Valerio Ganci ◽  
Mauro D’Onofrio ◽  
Edi Bon ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radio Emission ◽  
Spectral Properties ◽  
Main Sequence ◽  
Radio Detection ◽  
Thermal Origin ◽  
Cross Matching

AbstractWe analyze the optical properties of Radio-Loud quasars along the Main Sequence (MS) of quasars. A sample of 355 quasars selected on the basis of radio detection was obtained by cross-matching the FIRST survey at 20cm and the SDSS DR12 spectroscopic survey. We consider the nature of powerful emission at the high-Fe ii end of the MS. At variance with the classical radio-loud sources which are located in the Population B domain of the MS optical plane, we found evidence indicating a thermal origin of the radio emission of the highly accreting quasars of Population A.

scholarly journals The milliarcsecond-scale radio structure of AB Doradus A

2020 ◽  
Vol 641 ◽  
pp. A90
Author(s):  
J. B. Climent ◽  
J. C. Guirado ◽  
R. Azulay ◽  
J. M. Marcaide ◽  
D. L. Jauncey ◽  
...  
Keyword(s):  
Radio Emission ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Radio Structure ◽  
North West ◽  
Compact Source ◽  
The North ◽  
Polar Caps ◽  
Interacting Systems ◽  
Source Structure

Context. The fast rotator, pre-main sequence star AB Dor A is a strong and persistent radio emitter. The extraordinary coronal flaring activity is thought to be the origin of compact radio emission and other associated phenomena, such as large slingshot prominences. Aims. We aim to investigate the radio emission mechanism and the milliarcsecond radio structure around AB Dor A. Methods. We performed phase-referenced VLBI observations at 22.3 GHz, 8.4 GHz, and 1.4 GHz over more than one decade using the Australian VLBI array. Results. Our 8.4 GHz images show a double core-halo morphology, similar at all epochs, with emission extending at heights between 5 and 18 stellar radii. Furthermore, the sequence of the 8.4 GHz maps shows a clear variation of the source structure within the observing time. However, images at 1.4 GHz and 22.3 GHz are compatible with a compact source. The phase-reference position at 8.4 GHz and 1.4 GHz are coincident with those expected from the well-known milliarcsecond-precise astrometry of this star, meanwhile the 22.3 GHz position is 4σ off the prediction in the north-west direction. The origin of this offset is still unclear. Conclusions. We have considered several models to explain the morphology and evolution of the inner radio structure detected in AB Dor A. These models include emission from the stellar polar caps, a flaring, magnetically-driven loop structure, and the presence of helmet streamers. We also investigated a possible close companion to AB Dor A. Our results confirm the extraordinary coronal magnetic activity of this star, capable of producing compact radio structures at very large heights that have so far only been seen in binary interacting systems.

scholarly journals Radio Emission from Selected Algol Systems

1989 ◽  
Vol 107 ◽  
pp. 370-370
Author(s):  
G. Umana ◽  
S. Catalano ◽  
M. Rodonó ◽  
D. M. Gibson
Keyword(s):  
Radio Emission ◽  
Spectral Type ◽  
Evolutionary History ◽  
Binary Systems ◽  
Main Sequence ◽  
Close Binary ◽  
Close Binaries ◽  
Late Type ◽  
Close Binary Systems ◽  
Type Giant

Radio emission from close binary systems has long been detected in Algol and other systems. RS CVn systems have been found to be the most powerful and active. The RS CVn binaries are also known to show strong chromosferic and transition region emission line fluxes, that are one or two orders of magnitude higher than those from single stars of similar spectral type. This enhanced activity seems to be connected to the rapid rotation due to the tidal interaction in the system. The Algol binaries are semi-detected close binary systems formed by an early type main sequence primary and a late type giant secondary, while in the RS CVn both components are late type stars of about the same mass, the secondary being a giant or subgiant.The Algol binaries and RS CVn differ also in their evolutionary history. However, since the spectral type and probably the internal structure of the secondary components of Algols appear to be similar to that of the secondaries of RS CVn systems, and they both are synchronous fast rotators in close binaries, we would also expect that the secondaries of Algol systems to show some kind of activity.

scholarly journals Radio loudness along the quasar main sequence

2019 ◽  
Vol 630 ◽  
pp. A110 ◽  
Author(s):  
V. Ganci ◽  
P. Marziani ◽  
M. D’Onofrio ◽  
A. del Olmo ◽  
E. Bon ◽  
...  
Keyword(s):  
Black Hole ◽  
Radio Emission ◽  
Spectral Type ◽  
Main Sequence ◽  
Flux Ratio ◽  
Sloan Digital Sky Survey ◽  
Very Large Array ◽  
Black Hole Binaries ◽  
Line Region ◽  
Sky Survey

Context. When can an active galactic nucleus (AGN) be considered radio loud (RL)? Following the established view of the AGNs inner workings, an AGN is RL if associated with relativistic ejections emitting a radio synchrotron spectrum (i.e., it is a “jetted” AGN). In this paper we exploit the AGN main sequence that offers a powerful tool to contextualize radio properties. Aims. If large samples of optically-selected quasars are considered, AGNs are identified as RL if their Kellermann’s radio loudness ratio RK >  10. Our aims are to characterize the optical properties of different classes based on radio loudness within the main sequence and to test whether the condition RK >  10 is sufficient for the identification of RL AGNs, since the origin of relatively strong radio emission may not be necessarily due to relativistic ejection. Methods. A sample of 355 quasars was selected by cross-correlating the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters survey (FIRST) with the twelfth release of the Sloan Digital Sky Survey Quasar Catalog published in 2017. We classified the optical spectra according to their spectral types along the main sequence of quasars. For each spectral type, we distinguished compact and extended morphology (providing a FIRST-based atlas of radio maps in the latter case), and three classes of radio loudness: detected ( specific flux ratio in the g band and at 1.4 GHz, R′K < 10), intermediate (10 ≤ R′K < 70), and RL (R′K ≥ 70). Results. The analysis revealed systematic differences between radio-detected (i.e., radio-quiet), radio-intermediate, and RL classes in each spectral type along the main sequence. We show that spectral bins that contain the extreme Population A sources have radio power compatible with emission by mechanisms ultimately due to star formation processes. RL sources of Population B are characteristically jetted. Their broad Hβ profiles can be interpreted as due to a binary broad-line region. We suggest that RL Population B sources should be preferential targets for the search of black hole binaries, and present a sample of binary black hole AGN candidates. Conclusions. The validity of the Kellermann’s criterion may be dependent on the source location along the quasar main sequence. The consideration of the main sequence trends allowed us to distinguish between sources whose radio emission mechanisms is jetted from the ones where the mechanism is likely to be fundamentally different.

scholarly journals A Radio Survey of Older T Tauri Stars in the η Chamaeleontis Cluster

1999 ◽  
Vol 16 (3) ◽  
pp. 257-261 ◽  
Author(s):  
Eric E. Mamajek ◽  
Warrick A. Lawson ◽  
Eric D. Feigelson
Keyword(s):  
Radio Emission ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stars ◽  
Radio Continuum ◽  
Rotating Stars ◽  
Main Sequence Stars ◽  
X Ray ◽  
Rotation Periods ◽  
T Tauri

AbstractA radio continuum survey of X-ray-identified weak-lined T Tauri stars (WTTs) in the newly-discovered η Chamaeleontis cluster has been completed using the Australia Telescope Compact Array (ATCA). The 10 known WTTs in the cluster form a unique sample of codistant late-type pre-main-sequence stars with ages of ~8 Myr and masses ranging from 0·1–1·0 M⊙. Our survey detected none of the 10 X-ray-emitting WTTs with 3σ sensitivity limits at 4·8 and 8·6 GHz (6·2 and 3·5 cm) of typically 0·4 mJy, corresponding to a radio luminosity of 4·5 ×1015 erg Hz−1 s−1. Rotation periods for these stars indicate that they are not, as a group, fast-rotating stars. The non-detection in the radio bands supports the findings of other radio surveys of inhomogeneous samples of young stars, where radio emission is fairly common (10–30%) among very young T Tauri stars across all late spectral types, but confined to rapidly-rotating F-G-K stars amongst older zero-age main sequence stars. Rotation, more than youth, appears to be the key to radio emission in young stars.

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