J/ApJ/921/9 Ultra-wideband (0.4-4GHz) study of CU Vir (Das+, 2021)
Ultra-wideband, multiepoch radio study of the first discovered "main-sequence
radio pulse emitter" CU Vir.
Das B., Chandra P.
<Astrophys. J., 921, 9 (2021)>
=2021ApJ...921....9D 2021ApJ...921....9D
ADC_Keywords: Stars, variable; Stars, peculiar; Radio lines; Polarization
Keywords: Magnetic stars ; B stars ; Magnetospheric radio emissions ;
Astrophysical masers ; Radio astronomy ; Transient detection
Abstract:
The presence of a large-scale surface magnetic field in early-type
stars leads to several unique electromagnetic phenomena producing
radiation over X-ray to radio bands. Among them, the rarest type of
emission is electron cyclotron maser emission (ECME) observed as
periodic, circularly polarized radio pulses. The phenomenon was first
discovered in the hot magnetic star CU Vir. Past observations of this
star led to the consensus that the star produces only right circularly
polarized ECME, suggesting that only one magnetic hemisphere takes
part in the phenomenon. Here we present the first ultra-wideband
(0.4-4GHz) study of this star using the upgraded Giant Metrewave Radio
telescope and the Karl G. Jansky Very Large Array, which led to the
surprising discovery of ECME of both circular polarizations up to
around 1.5GHz. The GHz observations also allowed us to infer that the
upper ECME cutoff frequency is at ≥5GHz. The sub-GHz observation led
to the unexpected observation of more than two pairs of ECME pulses
per rotation cycle. In addition, we report the discovery of a "giant
pulse" and transient enhancements, which are potentially the first
observational evidence of "centrifugal breakout" of plasma from the
innermost part of the stellar magnetosphere. The stark contrast
between the star's behavior at GHz and sub-GHz frequencies could
either be due to propagation effects, a manifestation of varying
magnetic field topology as a function of height, or a signature of an
additional "ECME engine."
Description:
We observed the hot magnetic star CU Vir in band 3 (300-500MHz) and
band 4 (550-900MHz) of the upgraded Giant Metrewave Radio Telescope
(uGMRT) in 2019 January (epoch 1) and 2020 June (epoch 2), and in
bands L (1-2GHz) and S (2-4GHz) of the Karl G. Jansky Very Large Array
(VLA) in 2019 June and July. At all frequency bands, the star was
observed for one full rotation cycle.
Objects:
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RA (ICRS) DE Designation(s)
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14 12 15.80 +02 24 33.9 V* CU Vir = TYC 317-1590-1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 60 491 Flux density measurements at uGMRT Band 3 (300-500MHz)
table3.dat 60 4273 Flux density measurements at uGMRT Band 4 (550-900MHz)
table4.dat 59 2076 Flux density measurements at VLA L Band (1000-2000MHz)
table5.dat 59 2284 Flux density measurements at VLA S Band (2000-4000MHz)
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+, 2007-2017)
B/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-)
B/polarbase : PolarBase spectropol. database (ESPaDOnS, NARVAL) (Petit+, 2014)
J/A+AS/117/335 : Optical positions of radio emitting stars (Assafin+, 1996)
J/A+AS/130/215 : Effective temperatures of Ap stars (Sokolov, 1998)
J/A+A/383/1062 : Opt. positions of 55 radio stars at Yunnan Obs. (Hu+, 2002)
J/A+A/493/931 : MAD observations of σ Ori (Bouy+, 2009)
J/MNRAS/431/2106 : CU Vir Stroemgren differential photometry (Pyper+, 2013)
J/MNRAS/431/2240 : Activity in A-type stars from Kepler (Balona, 2013)
J/PASP/126/469 : PolarBase catalogue of stellar spectra (Petit+, 2014)
J/A+A/625/A34 : Photometry of CU Vir (Krticka+, 2019)
J/MNRAS/499/5379 : Longitudinal magnetic field of 6 B stars (Shultz+, 2020)
J/MNRAS/504/3730 : Synthetic RGB photometry of bright stars (Cardiel+, 2021)
J/A+A/652/A31 : Stellar magnetic rot. phase curves. II (Bychkov+, 2021)
Byte-by-byte Description of file: table[2345].dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d HJD1 Heliocentric Julian Day, observation start
16- 29 F14.6 d HJD2 Heliocentric Julian Day, observation end
31- 36 F6.2 mJy Flux [-1.9/184] Flux density in Band
38- 42 F5.2 mJy e_Flux [0.2/19] Uncertainty in Flux (1)
44- 46 A3 --- Pol Polarization type ("RCP"; "LCP") (2)
48- 53 F6.1 MHz nu0 [347/3947] Central frequency of a band
55- 60 F6.1 MHz dnu [22/1128] Bandwidth
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Note (1): Error includes the fitting error, image rms and the uncertainty
involved in absolute flux density calibration.
Note (2): RCP and LCP (right and left circular polarization respectively) are
in accordance with IAU/IEEE convention.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Feb-2023