Mid-infrared variations of R Coronae Borealis stars

Rao, N. Kameswara; Lambert, David L.

doi:10.1093/mnras/stu2748

Cited by 8 publications

(8 citation statements)

References 49 publications

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“…In Figure 11, we plot the periods of these stars against their effective temperatures. This figure is similar to Figure 32 of Lawson et al (1990) and Figure 15 of Rao & Lambert (2015). Clayton et al (2003) showed that most (if not all) RCB stars have winds.…”

Section: Pulsation Periods and Effective Temperaturessupporting

confidence: 88%

Census of R Coronae Borealis Stars. I. Infrared Light Curves from Palomar Gattini IR

Karambelkar

Kasliwal

Tisserand

et al. 2021

ApJ

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We are undertaking the first systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, beginning with IR light curves from the Palomar Gattini IR (PGIR) survey. The PGIR is a 30 cm J-band telescope with a 25 deg 2 camera that is surveying 18,000 deg 2 of the northern sky (δ > −28°) at a cadence of 2 days. We present PGIR light curves for 922 RCB candidates selected from a mid-IR color-based catalog. Of these 922, 149 are promising RCB candidates, as they show pulsations or declines similar to RCB stars. The majority of the candidates that are not RCB stars are either long-period variables (LPVs) or RV Tauri stars. We identify IR color-based criteria to better distinguish between RCB stars and LPVs. As part of a pilot spectroscopic run, we obtain NIR spectra for 26 of the 149 promising candidates and spectroscopically confirm 11 new RCB stars. We detect strong He I λ10830 features in the spectra of all RCB stars, likely originating within high-velocity (200-400 km s −1 ) winds in their atmospheres. Nine of these RCB stars show 12 C 16 O and 12 C 18 O molecular absorption features, suggesting that they are formed through a white dwarf merger. We detect quasiperiodic pulsations in the light curves of five RCB stars. The periods range between 30 and 125 days and likely originate from the strange-mode instability in these stars. Our pilot run results motivate a dedicated IR spectroscopic campaign to classify all RCB candidates.Unified Astronomy Thesaurus concepts: R Coronae Borealis variable stars (1327); Hydrogen deficient stars (769); Near infrared astronomy (1093); Time domain astronomy (2109)

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Section: Pulsation Periods and Effective Temperaturessupporting

confidence: 88%

Census of R Coronae Borealis Stars. I. Infrared Light Curves from Palomar Gattini IR

Karambelkar

Kasliwal

Tisserand

et al. 2021

ApJ

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“…There are other R CrB stars which are known or suspected to pulsate. Rao and Lambert (2015) list 29. Most if not all of them have pulsation amplitudes which are even smaller than that of RY Sgr, so it will be almost impossible to study their pulsation with visual data.…”

Section: Discussionmentioning

confidence: 99%

A Study of Pulsation and Fadings in some R Coronae Borealis Stars

Percy,

Dembski

2018

Preprint

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We have measured the times of onset of recent fadings in four R CrB stars -V854 Cen, RY Sgr, R CrB, and S Aps. These times continue to be locked to the stars' pulsation periods, though with some scatter. In RY Sgr, the onsets of fading tend to occur at or a few days after pulsation maximum. We have studied the pulsation properties of RY Sgr through its recent long maximum using (O-C) analysis and wavelet analysis. The period "wanders" by a few percent. This wandering can be modelled by random cycle-to-cycle period fluctuations, as in some other types of pulsating stars. The pulsation amplitude varies between 0.05 and 0.25 in visual light, non-periodically but on a time scale of about 20 pulsation periods.

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“…These puffs can be detected in the IR. Recent studies pertaining to IR variability of RCB stars has found that the covering factor can vary from RCB star to RCB star and find an average covering factor of 0.28±0.04 for R CrB (García-Hernández, Rao & Lambert 2011b;Rao & Lambert 2015). Other studies find a higher covering factor (Hecht et al 1984;Clayton et al 1999).…”

Section: Mass Loss From a White Dwarf Merger?mentioning

confidence: 99%

What Is the Shell Around R Coronae Borealis?

Montiel

Clayton

Marcello

et al. 2015

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The hydrogen-deficient, carbon-rich R Coronae Borealis (RCB) stars are known for being prolific producers of dust which causes their large iconic declines in brightness. Several RCB stars, including R CrB, itself, have large extended dust shells seen in the far-infrared. The origin of these shells is uncertain but they may give us clues to the evolution of the RCB stars. The shells could form in three possible ways. 1) they are fossil Planetary Nebula (PN) shells, which would exist if RCB stars are the result of a final, helium-shell flash, 2) they are material left over from a white-dwarf merger event which formed the RCB stars, or 3) they are material lost from the star during the RCB phase. Arecibo 21-cm observations establish an upper limit on the column density of H I in the R CrB shell implying a maximum shell mass of 0.3 M . A low-mass fossil PN shell is still a possible source of the shell although it may not contain enough dust. The mass of gas lost during a white-dwarf merger event will not condense enough dust to produce the observed shell, assuming a reasonable gas-to-dust ratio. The third scenario where the shell around R CrB has been produced during the star's RCB phase seems most likely to produce the observed mass of dust and the observed size of the shell. But this means that R CrB has been in its RCB phase for ∼10 4 yr.

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Mid-infrared variations of R Coronae Borealis stars

Cited by 8 publications

References 49 publications

Census of R Coronae Borealis Stars. I. Infrared Light Curves from Palomar Gattini IR

Census of R Coronae Borealis Stars. I. Infrared Light Curves from Palomar Gattini IR

A Study of Pulsation and Fadings in some R Coronae Borealis Stars

What Is the Shell Around R Coronae Borealis?

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