The Spatial Size of the SiO Masers in R Leonis Derived from Lunar Occultations

Cernicharo, J.; Brunswig, W.; Paubert, G.; Liechti, S.

doi:10.1086/187257

Cited by 12 publications

(14 citation statements)

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“…Previous VLBI observations of R Leonis were made by Colomer et al (1992); a lunar occultation experiment is reported by Cernicharo et al (1994). Danchi et al (1994) measured the radius of the inner radius of the dust shell to be 0.…”

Section: R Leonismentioning

confidence: 99%

VLBA observations of SiO masers towards Mira variable stars

Cotton¹,

Mennesson²,

Diamond³

et al. 2004

A&A

103

122

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Abstract. We present new total intensity and linear polarization VLBA observations of the ν = 2 and ν = 1 J = 1−0 maser transitions of SiO at 42.8 and 43.1 GHz in a number of Mira variable stars over a substantial fraction of their pulsation periods. These observations were part of an observing program that also includes interferometric measurements at 2.2 and 3.6 micron (Mennesson et al. 2002); comparison of the results from different wavelengths allows studying the envelope independently of the poorly known distances to these stars. Nine stars were observed at from one to four epochs during 2001. The SiO emission is largely confined to rings which are smaller than the inner radius of the dust shells reported by Danchi et al. (1994). Two stars (U Orionis, R Aquarii) have maser rings with diameters corresponding to the size of the hot molecular layer as measured at 3.6 micron; in the other cases, the SiO rings are substantially larger. Variations of ring diameter for most, but not all stars, had an rms amplitude in agreement with the models of Humphreys et al. (2002) although the expected relationship between the diameter and pulsation phase was not seen. The ring diameter in U Orionis shows remarkably small variation. A correlation between the 2.2/3.6 µm diameter ratio with that of the SiO/3.6 µm diameter ratio is likely due to differences in the opacities at 2.2 and 3.6 µm in a molecular layer. A further correlation with the inner size of the dust shell reported by Danchi et al. (1994) suggest some differences in the temperature structure. Clear evidence is seen in R Aquarii for an equatorial disk similar to that reported by Hollis et al. (2001); rotation is possibly also detected in S Coronae Boralis.

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Section: R Leonismentioning

confidence: 99%

VLBA observations of SiO masers towards Mira variable stars

Cotton¹,

Mennesson²,

Diamond³

et al. 2004

A&A

103

122

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“…A separate, high resolution measurement of R Leo was made during a lunar occultation (Cernicharo et al 1994) in the (J = 2 → 1)-line in v = 1 at 86 GHz, a frequency not yet reached by VLBI measurement techniques. Of course, occultation gives high resolution only in one dimension.…”

Section: Interferometrymentioning

confidence: 99%

Circumstellar envelopes and Asymptotic Giant Branch stars

Habing

1996

The Astron Astrophys Rev

447

444

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Red giants are sometimes surrounded by envelopes, the result of the ejection of stellar matter at a large rate (Ṁ> 10 −7 M /yr) and at a low velocity (10 km/s). In this review the envelopes are discussed and the relation between stars and envelope: what stars combine with what envelopes?The envelope emits radiation by various processes and has been detected at all wavelengths between the visual and the microwave range. I review the observations of continuum radiation emitted by dust particles and of rotational transitions of molecules, where these molecules have been excited by thermal or by non-thermal ("maser") processes. I discuss mainly the oxygen-rich stars, those of spectral type M, and only briefly the closely related carbon-rich stars.By and large the density in the envelope is well described by spherically symmetric outflow at a constant velocity; on the time scale needed to flow from stellar surface to the outermost layers, i.e. 10 5 yr, the loss of mass is sometimes interrupted suddenly after which the envelope becomes "detached" from the star. The temperature decreases when moving outward; heat input is by friction between dust particles and gas and cooling occurs by line radiation by various molecules, especially by H 2 O. The molecular composition is determined by formation in an equilibrium process deep in the atmosphere and by destruction in the outer parts of the outflow by interstellar UV radiation (H 2 , CO, H 2 O) or by depletion due to condensation on dust grains (SiO); dust particles of silicate material solidify where the radiation temperature is decreased to about 1000 K, and this is at a few stellar radii.The various continuum spectra produced by the dust particles in different stars are well modelled by a simple model of the density and dust temperature distribution plus the assumption that the particles consist of "dirty silicate", i.e. silicate with Fe and Al ions added. A large range of optical depths, τ 9.7µm , is observed: from 0.01 to 10. In envelopes with large optical depth the star itself can no longer be detected directly. Model calculations also show that the momentum in the outflow, i.e.Ṁ .v out is provided by radiation pressure on the dust particles followed by the complete transfer of this momentum to the gas. The mass-loss rate itself,Ṁ , is not determined by radiation pressure but by dynamic processes in the region below the 98 H.J. Habing dust condensation layer. When τ 9.7µm is sufficiently large its measurement, that of the stellar luminosity, L * and that of the outflow velocity, v out , permit the determination ofṀ , i.e. the total outflow rate, without making assumptions about the abundance of the dust particles or of the molecular gases. Detached envelopes have been seen in a few cases.Thermal molecular radiation is faint compared to the maser emission but has been measured in distant stars, e.g. in stars near the galactic center. Different molecules outline different "spheres" around the star. The largest sphere (a radius of 0.1 pc) is outlined by an emission line...

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“…The most recent observational results on the morphology are the interferometric observations presented in Sánchez-Contreras & Sahai, 2004. Concerning the chemical composition, a line survey from 80 to 275 GHz has been recently completed (Cernicharo et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Observational Evidence of the Formation of Cyanopolyynes in CRL 618 through the Polymerization of HCN

Pardo¹,

Cernicharo²,

Goicoechea

2005

ApJ

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The abundance ratio of consecutive members of the cyanopolyynes family has been explored in CRL618 using data acquired in a complete line survey covering the frequency range 81-356 GHz. The J up range explored for the different molecules is the following: 1 to 4 for HCN and HNC, 9 to 39 for HC 3 N, 31 to 133 for HC 5 N, and 72 to 85 for HC 7 N (not detected beyond J up =85). The lowest vibrationally excited state of HC 7 N (ν 15 at 62 cm −1 ) has been tentatively detected. Data analysis has been performed by extending our previous geometrical and radiative transfer model of the slowly expanding envelope (SEE) surrounding the compact central continuum source of CRL 618, that was established from the study of rotational lines in several vibrationally excited states of HC 3 N. The new lines analyzed here require to model the high velocity wind (HVW) component and the colder circumstellar gas, remnant of the AGB phase of CRL618. The derived HC 3 N/HC 5 N and HC 5 N/HC 7 N abundance ratios from this set of uniformly calibrated lines are between ∼ 3 and 6 in the different regions, similar to standard values in the CSM and ISM, and consistent with previous estimates obtained from ISO observations and chemical models. However, the abundance ratios of HC 3 N, HC 5 N and HC 7 N with respect to HCN are at least two orders of magnitude larger than those typical for AGB C-rich stars, such as IRC+10216. This fact indicates that, in the short transition toward the Planetary Nebula phase, HCN is quickly reprocessed into longer cyanopolyyne chains. A similar behavior was previously found in this object for the polyacetylenic chains (C 2n H 2 ).

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The Spatial Size of the SiO Masers in R Leonis Derived from Lunar Occultations

Cited by 12 publications

References 0 publications

VLBA observations of SiO masers towards Mira variable stars

VLBA observations of SiO masers towards Mira variable stars

Circumstellar envelopes and Asymptotic Giant Branch stars

Observational Evidence of the Formation of Cyanopolyynes in CRL 618 through the Polymerization of HCN

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