J/A+A/699/A326      R Cas, o Cet, and R Leo 22GHz spectra         (Brand+, 2025)

Water vapour masers in long-period variable stars. IV. Mira variables R Cas, o Cet and R Leo. Brand J., Engels D., Zanichelli A., Etoka S. <Astron. Astrophys. 699, A326 (2025)> =2025A&A...699A.326B 2025A&A...699A.326B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Masers ; Spectra, radio Keywords: masers - stars: AGB and post-AGB circumstellar matter - Abstract: We carry out decades-long single-dish monitoring of the variation in water-maser emission associated with the circumstellar envelopes (CSEs) of different types of evolved stars. We follow the variation in the maser emission over long time intervals (multiple optical periods) to understand the structure and kinematics of the stellar wind that drives the maser clouds away from the star. We also determine how this may depend on the stellar properties. We carried out monitoring campaigns with single-dish telescopes of water-maser emission at 22GHz in the CSEs of four stars: o Cet, R Leo, chi Cyg, and R Cas. The observations took place with some interruptions between 1987 and 2023. The exact time interval differed from one star to the next, but no star was monitored for fewer than 15∼years. The variability in integrated flux in the masers in R Cas and o Cet followed the variability in the optical with the same period, but with a lag of about one-third in phase. R Leo was too often below our sensitivity threshold for us to determine a radio period. Remarkably, no maser at all was detected in chi Cyg. The variability in the masers in R Cas has a distinctive pattern. The total flux, modulated by the pulsations of the star, gradually increases to a maximum, which is followed by a similar decrease. This takes about 20∼years. The pattern is repeated after an interval of quiescence of several years. Our observations have covered about one and a half cycle of this pattern so far. During its decline from a maximum, the variation in the flux resembles a damped harmonic oscillator. There are two dominant emission components that move almost tangentially on either side of the star with respect to the observer. The redshifted component likely originates from a single cloud and seems to be falling back towards the star. The blue component, moving in the CSE hemisphere nearest to us, has no drift in the line-of-sight velocity and appears to originate in a time series of short-living clouds with line-of-sight velocities within ∼1km/s of each other. No systematic velocity drifts are found in RLeo and oCet. A few bursts of emission were detected at infrequent times in RCas and RLeo that lasted about a year and caused an increase in the flux density by 1-2 orders of magnitude. The velocity range of the maser emission is <10km/s, which is narrower than the majority of the Miras and semi-regular variables we studied so far. In particular, in the stars with a low bolometric luminosity, o Cet and R Leo, only the brightest maser components from a limited part of the CSE are visible. The existence of a zone in the CSE with favourable conditions for maser excitation is confirmed most clearly in the case of R Cas through the unique pattern of its maser variability. The bolometric luminosity of a star and the velocity range of its water-maser emission, that is, the number of emission components in the spectra, are clearly correlated. Most maser components in the CSEs we studied originated in clouds that move almost perpendicular to the line of sight. The redshifted emission in R Cas is consistent with an origin in a single cloud that lived for at least about eight years. Description: The FITS files are the spectra of the 22 GHz water maser emission of RCas (N=160), oCet (N=128) and RLeo (N=99) as shown in Figs. A1, A2 and A3 in the Appendix of the paper (available on Zenodo: https://zenodo.org/records/15534987). Flux density in Jy versus the line-of-sight velocity relative to the LSR (Vlos) in m/s (fits header; km/s on Zenodo). The observations were made with the 32m Medicina antenna and the 100m telescope at Effelsberg. The spectra were originally in CLASS-format and were transformed to FITS via the command 'fits write name.fits /mode spectrum' in CLASS. CLASS is part of the Grenoble GILDAS software package. The file names consist of the name of the star, followed by a running number, and finally by the TJD (truncated Julian Date, TJD=JD-2440000.5) Objects: ----------------------------------------- RA (2000) DE Designation(s) ----------------------------------------- 02 19 20.8 -02 58 37 o Cet = V* o Cet 09 47 33.5 +11 25 44 R Leo = V* R Leo 23 58 24.7 +51 23 20 R Cas = V* R Cas ----------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file list.dat 106 387 List of spectra fits/* . 387 Individual fits spectra -------------------------------------------------------------------------------- See also: J/A+A/644/A45 : R Crt & RT Vir Medicina & Effelsberg spectra (Brand+, 2020) J/A+A/686/A251 : U Her & RR Aql Medicina & Effelsberg spectra (Winnberg+ 2024) Byte-by-byte Description of file: list.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 9 F9.5 deg RAdeg Right Ascension of center (J2000) 10- 18 F9.5 deg DEdeg Declination of center (J2000) 21- 23 I3 --- Nx Number of pixels along X-axis 25- 47 A23 "datime" Obs.date Observation date 49- 60 E12.6 Hz bFREQ Lower value of frequency interval 62- 73 E12.6 Hz BFREQ Upper value of frequency interval 75- 82 F8.2 Hz dFREQ Number of pixels along U-axis 85- 86 I2 Kibyte size Size of FITS file 88-106 A19 --- FileName Name of FITS file, in subdirectory fits -------------------------------------------------------------------------------- Acknowledgements: Jan Brand, brand(at)ira.inaf.it Dieter Engels, dieter.engels(at)uni-hamburg.de References: Winnberg et al., Paper I 2008A&A...482..831W 2008A&A...482..831W (RX Boo and SV Peg) Brand et al., Paper II 2020A&A...644A..45B 2020A&A...644A..45B (R Crt and RT Vir), Cat. J/A+A/644/A45 Winnberg et al., Paper III 2024A&A...686A.251W 2024A&A...686A.251W (U Her and RR Aql), Cat. J/A+A/686/A251
(End) Patricia Vannier [CDS] 22-Jun-2025
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