Discovery of Two New HCN Maser Lines in Five Carbon Stars

Bieging, John H.

doi:10.1086/319130

Cited by 21 publications

(22 citation statements)

References 16 publications

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“…Bieging 2001;Schilke & Menten 2003). Table 2 summarizes the different HCN transitions that can be observed as maser emission in the submillimetre wavelength regime (Müller et al 2001).…”

Section: Hcnmentioning

confidence: 99%

Linear polarization of submillimetre masers

Pérez-Sánchez

Vlemmings

2013

A&A

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Context. Once ALMA full polarization capabilities are offered, it will become possible to perform detailed studies of polarized maser emission towards star-forming regions and late-type stars, such as (post-) asymptotic giant branch stars and young planetary nebulae. To derive the magnetic field orientation from maser linear polarization, a number of conditions involving the rate of stimulated emission R, the decay rate of the molecular state Γ, and the Zeeman frequency gΩ need to be satisfied. Aims. The goal of this work is to investigate if SiO, H 2 O and HCN maser emission within the ALMA frequency range can be detected with observable levels of fractional linear polarization in the regime where the Zeeman frequency is greater than the stimulated emission rate. Methods. We used a radiative transfer code to calculate the fractional linear polarization as a function of the emerging brightness temperature for a number of rotational transition of SiO, H 2 O and HCN that have been observed to display maser emission at submillimetre wavelengths. We assumed typical magnetic field strengths measured towards galactic star-forming regions and circumstellar envelopes of late-type stars from previous VLBI observations. Since the Landé g-factors have not been reported for the different rotational transitions we modelled, we performed our calculations assuming conservative values of the Zeeman frequency for the different molecular species. Results. Setting a lower limit for the Zeeman frequency that still satisfies the criteria gΩ > R and gΩ > Γ, we find fractional polarization levels of up to 13%, 14% and 19% for the higher J transitions analysed for SiO, H 2 O and HCN, respectively, without considering anisotropic pumping or any other non-Zeeman effect. These upper limits were calculated assuming a magnetic field oriented perpendicular to the direction of propagation of the maser radiation. Conclusions. According to our results, SiO, H 2 O, and HCN maser emission within the ALMA frequency range can be detected with suitable linear polarization to trace the magnetic field structure towards star-forming regions and late-type stars even if the detected polarization has been enhanced by non-Zeeman effects.

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“…Bieging 2001;Schilke & Menten 2003). Table 2 summarizes the different HCN transitions that can be observed as maser emission in the submillimetre wavelength regime (Müller et al 2001).…”

Section: Hcnmentioning

confidence: 99%

Linear polarization of submillimetre masers

Pérez-Sánchez

Vlemmings

2013

A&A

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“…Refs. -1) This paper; 2) Schöier & Olofsson (2001); 3) Olofsson et al (1996); 4) Olofsson et al (1993b); 5) ; 6) JCMT public archive; 7) Bieging (2001 …”

Section: Continuum Observationsunclassified

Properties of detached shells around carbon stars

Schöier¹,

Lindqvist

Olofsson³

2005

A&A

159

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Abstract. The nature of the mechanism responsible for producing the spectacular, geometrically thin, spherical shells found around some carbon stars has been an enigma for some time. Based on extensive radiative transfer modelling of both CO line emission and dust continuum radiation for all objects with known detached molecular shells, we present compelling evidence that these shells show clear signs of interaction with a surrounding medium. The derived masses of the shells increase with radial distance from the central star while their velocities decrease. A simple model for interacting winds indicates that the mass-loss rate producing the faster moving wind has to be almost two orders of magnitudes higher (∼10 −5 M yr −1 ) than the slower AGB wind (a few 10 −7 M yr −1 ) preceding this violent event. At the same time, the present-day mass-loss rates are very low indicating that the epoch of high mass-loss rate was relatively short, on the order of a few hundred years. This, together with the number of sources exhibiting this phenomenon, suggests a connection with He-shell flashes (thermal pulses). We report the detection of a detached molecular shell around the carbon star DR Ser, as revealed from new single-dish CO (sub-)millimetre line observations. The properties of the shell are similar to those characterising the young shell around U Cam.

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“…The HCN molecule can be used to trace many region of the ISM since it is one of the most observed molecules in space. HCN has been observed in comets (Huebner, Buhl & Snyder 1974; Irvine et al 1996), planetary atmospheres (Hidayat et al 1997), molecular clouds (Turner, Pirogov & Minh 1997; Hatchell, Millar & Rodgers 1998; Hirota et al 1998), carbon star atmospheres (Aoki, Tsuji & Ohnaka 1998; Bieging, Shaked & Gensheimer 2000; Harris et al 2003) and circumstellar masers (Bieging 2001). Since collisions compete with radiative processes in altering populations in molecular rovibrational levels, the accurate estimation of physical and chemical conditions in the ISM from spectral line data depends on accurate collisional rate coefficients with the most abundant interstellar species (He and H 2 ).…”

Section: Introductionmentioning

confidence: 99%

Hyperfine excitation of HCN by H2 at low temperature

Abdallah¹,

Najar²,

Jaı̈dane³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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Modelling of molecular emission spectra from interstellar clouds requires the calculation of rate coefficients for (de‐)excitation by collisions with the most abundant species. We calculate rate coefficients for the rotational and hyperfine (de‐)excitation of the hydrogen cyanide (HCN) by collisions with H2 (j= 0), the most abundant collisional partner in cold molecular clouds. The scattering calculations are based on a new ab initio potential energy surface for the HCN–H2 collisional system, averaged over the H2 orientations. Close‐coupling calculations of pure rotational cross‐sections are performed for levels up to j= 10 and for total energies up to 1000 cm−1. The hyperfine cross‐sections are then obtained using a recoupling technique. The rotational and hyperfine cross‐sections are used to determine collisional rate coefficients for temperatures ranging from 5 to 100 K. A clear propensity rule in favour of even Δj rotational transitions is observed. The usual Δj=ΔF propensity rules are observed for the hyperfine transitions. The new rate coefficients are compared with the previous results obtained for the HCN molecule. Significant differences are found, mainly due to the use of H2 as a collisional partner instead of He. The new rate coefficients will significantly help in interpreting HCN emission lines observed with current and future telescopes.

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Discovery of Two New HCN Maser Lines in Five Carbon Stars

Cited by 21 publications

References 16 publications

Linear polarization of submillimetre masers

Linear polarization of submillimetre masers

Properties of detached shells around carbon stars

Hyperfine excitation of HCN by H2 at low temperature

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