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Gas Infall and Possible Circumstellar Rotation in R Leonis? J A&A 622, L14 (2019) Astronomy https://doi.org/10.1051/0004-6361/201834840 & c ESO 2019 Astrophysics LETTER TO THE EDITOR Gas infall and possible circumstellar rotation in R Leonis? J. P. Fonfría1, M. Santander-García2, J. Cernicharo1, L. Velilla-Prieto3, M. Agúndez1, N. Marcelino1, and G. Quintana-Lacaci1 1 Molecular Astrophysics Group, Instituto de Física Fundamental, CSIC, C/ Serrano, 123, 28006 Madrid, Spain e-mail: [email protected] 2 Observatorio Astronómico Nacional, OAN-IGN, Alfonso XII, 3, 28014 Madrid, Spain 3 Dept. of Space, Earth, and Environment, Astronomy and Plasma Physics Division, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden Received 12 December 2018 / Accepted 6 February 2019 ABSTRACT We present new interferometer molecular observations of R Leo taken at 1.2 mm with the Atacama Large Millimeter Array with an angular resolution up to '000: 026. These observations permitted us to resolve the innermost envelope of this star, which revealed a complex structure that involves extended continuum emission and molecular emission showing a non-radial gas velocity distribu- tion. This molecular emission displays prominent red-shifted absorptions located immediately in front of the star, which are typical footprints of material infall. This emission also shows lateral gas motions compatible with a torus-like structure. Key words. stars: AGB and post-AGB – stars: individual: R Leo – circumstellar matter – stars: mass-loss – techniques: interferometric – techniques: high angular resolution 1. Introduction In this Letter, we present new interferometer observations of 29 R Leo is an O-rich asymptotic giant branch star (AGB) CO and SiO towards the AGB star R Leo. They were carried out with the Atacama Large Millimeter Array (ALMA) with an located at '70−85 pc from Earth (De Beck et al. 2010; 00 Ramstedt & Olofsson 2014). It has an effective temperature of angular resolution of up to 0: 026, which is comparable to the size '2500−3000 K and an angular diameter of '000: 025−000: 030 in the of the star. K band (Perrin et al. 1999; Fedele et al. 2005; Wittkowski et al. 2016). It pulsates with a period of '310 days, ejecting pro- 2. Observations −7 −1 cessed material with a low mass-loss rate of '1:0×10 M yr and a terminal velocity of 6−9 km s−1 (Bujarrabal et al. 1994; We observed R Leo with ALMA during Cycles 4 and 5 within Cernicharo et al. 1997). the frame of project 2016.1.01202.S. Array configurations C40- The continuum at different wavelengths (optical, infrared, 2, C40-5, C40-6, and C43-9 were used and provided baselines and millimeter) together with the thermal and maser molecular from 15 m up to 13.9 km. These observations give a complete ' emissions coming from this star have been analysed with dif- view of the envelope of R Leo at different scales along 1:25 pul- ferent observing techniques (e.g. Castelaz & Luttermoser 1997; sation periods. The observation details can be found in Table1. Pardo et al. 1998; Ryde et al. 1999; González-Delgado et al. Four spectral windows covered the frequency ranges − − 2003; Soria-Ruiz et al. 2007). Some of these observations 212:7 216:8 and 227:5 231:5 GHz with a channel width of suggested the existence of complex structures in the innermost 488 kHz. The flux, bandpass, and pointing were calibrated in the envelope. Cernicharo et al.(1994) carried out lunar occultation usual way by observing J0854+2006 or J1058+0133. We esti- ' observations of the SiO(v = 1; J = 2−1) maser, finding a low- mate a flux error 5%. The phase calibrators and check sources velocity structure within the 000: 5 sized region around the star that J1002+1216, J1008+0621, and J0946+1017 were periodically could be interpreted as a developing bipolar outflow or a rotating observed. R Leo was observed twice with configuration C43-9. torus. However, the limited spatial information perpendicular to In the first run (run A), the baseline of one spectral window was the occultation direction achieved was insufficient to properly affected by strong spurious periodic spikes, the weather was not ' constrain this structure. Additional asymmetries were found good enough for this demanding configuration (PWV 1.2 mm), at larger scales by Plez & Lambert(1994), suggesting that the and the uv plane coverage was limited. The data quality greatly structure revealed by Cernicharo et al.(1994) could be part of a increased during the second run (run B), and run A was depre- larger structure that covers a significant fraction of the envelope. cated. The data were calibrated with the pipeline in CASA 4.7.2 (McMullin et al. 2007). ? This paper makes use of the following ALMA data: Mapping and data analysis were almost fully performed with ADS/JAO.ALMA#2016.1.01202.S. ALMA is a partnership of GILDAS1. The images were restored adopting a robust parame- ESO (representing its member states), NSF (USA) and NINS (Japan), ter of 1.0 and 0.1 (natural and uniform weighting, hereafter). We together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. 1 https://www.iram.fr/IRAMFR/GILDAS Article published by EDP Sciences L14, page 1 of5 A&A 622, L14 (2019) Table 1. Observation summary. Conf./Run Date Phase PSF W MRS Continuum Gaussian Fit HPBW PA Peak Integral Peak D. FWHM D. PA (00 × 00) (deg) (00) ( mJy beam−1) (mJy) ( mJy beam−1)(00 × 00) (deg) C40-2 2017-Mar-22 0.80 1:560 × 1:080a 80 N 11.6 91:16 ± 0:12 105:8 ± 0:6 – – – C40-5 2017-May-03 0.94 0:387 × 0:359b 45 N 4.5 91:10 ± 0:16 111:6 ± 1:1 – – – C40-6 2016-Oct-01 0.25 0:186 × 0:157c 32 N 1.6 101:0 ± 0:3 140:2 ± 2:1 – – – C43-9/A 2017-Sep-21 0.40 0:096 × 0:035d 45 N 0.4 68:19 ± 0:20 103:1 ± 1:6 – – – 0:071 × 0:025e 32 U 52:55 ± 0:18 103:3 ± 1:8 – – – C43-9/B 2017-Oct-27 0.50 0:060 × 0:046 f 134 N 0.6 45:10 ± 0:21 90 ± 3 37.8 0:042 × 0:034 173 7.7 0:190 × 0:021 50 0:026 × 0:026g – U 21:38 ± 0:16 85 ± 3 16.5 0:045 × 0:030 155 5.4 0:132 × 0:022 50 Notes. From left to right, the columns contain the ALMA configuration and the run for duplicated observations, the observation date, the optical pulsation phase (pulsation period = 310 days; JDmax = 2457896 following AAVSO (https://www.aavso.org/)), the size and PA of the synthe- sised PSF, the visibility weighting (N, “natural”, means robust = 1 and U, “uniform”, robust = 0.1 in GILDAS), the maximum recoverable scale, the continuum peak for every configuration, the continuum integral above the 5σ level contours, the peak emission of the Gaussian components of the fit, and the FWHM and PA after deconvolution. When the Gaussian fit is not provided (–), the source can be considered as point-like. The errors of the continuum peak and the continuum integral do not consider the flux calibration uncertainties. The statistical errors of the Gaussian fit (a−g) 00 00 00 00 00 00 00 are always .5%. The characteristic HPBWs, θPSF, are 1: 30, 0: 37, 0: 17, 0: 058, 0: 042, 0: 052, and 0: 026, respectively. estimate a positional uncertainty for the highest angular resolu- tion of '000: 005 from the standard deviation of the emission peak position of the phase calibrator over time (Menten et al. 2006; Fonfría et al. 2014). In this Letter, we focuse on the short-scale observations to describe the stellar vicinity. The analysis of the envelope through the larger-scale maps is beyond the scope of this work and will be presented elsewhere (Fonfría et al., in prep.). Owing to the stellar pulsation phase incoherence and the long time lag ('1:1 yr), the data taken with the C40-6 and C43-9 configurations were not merged to prevent artefacts. 3. Results and discussion 3.1. Structure of the continuum emission The observations show one continuum emission source in the region of the sky that is covered by the primary beam (Fig.1). It peaks at (RA, Dec)=(09h47m33:s4915 ± 0:s0004; 11◦2504200: 899 ± 000: 005). The highest resolution observations show a compact source surrounded by a faint extended brightness distribution elongated roughly along the northeast-southwest direction (Fig.1). It is noteworthy that the maximum recoverable scale (MRS; '000: 6) is similar to the size of the extended emission in Fig.1, which is '000: 35 above the 5σ level. Thus, the array could be filtering emission, which would prevent us from deriving reliable bright- ness temperatures for the star. Fig. 1. Continuum emission observed with configuration C43-9, run B, 00 The continuum emission can be described by two Gaussian- assuming natural weighting (lower panel; θPSF ' 0: 052) and uniform 00 like components: one compact and one extended component weighting (upper panel; θPSF ' 0: 026). The lowest contours are at ±5σ (Table1). We can estimate the size of the continuum source (2.3% and 3.75% of the maximum for the lower and upper insets). The at 7 mm at the same pulsation phase as during our observa- rest are at 5, 10, 30, 50, 70, and 90% of the maximum. The grey crosses tions ('0:50) from the results reported by Matthews et al.(2018) indicate where the emission peaks in the uniformly weighted map.
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