PoS(IX EVN Symposium)057 O × 2 kpc. 0.5) 11 09 . . 0 0 ± + − http://pos.sissa.it/ 2) masers around = v etical evolutionary model Our astrometric monitoring 1 and -estimated to be (3 = Ma. Using our newly obtained v nd absolute positions of the H the Golden Age for Radio Astronomy al structure and kinematics of the s suggest a bipolar outflow around 0, − 1 = J O and SiO ( 2 e Commons Attribution-NonCommercial-ShareAlike Licence. 0.08 mas, and it corresponds to a distance of 1.14 ± ∗ . This improved luminosity is more consistent with the theor ⊙ L [email protected] [email protected] [email protected] [email protected] 5 VY CMa along the line of sight. and SiO masers. The 3-dimensional structures and kinematic VY Canis Majoris (VY CMa) carried outmeasured with VERA a for parallax 13 months. of 0.88 10 This is the first trigonometricdistance parallax with a measurement high for accuracy, VY the C luminosity of VY CMa was re than previous values. Moreover,circumstellar we envelopes considered around VY 3-dimension CMa with proper motions a Speaker. We report on observational results of H ∗ Copyright owned by the author(s) under the terms of the Creativ c The 9th European VLBI Network Symposiumand on EVN The Users role Meeting of VLBISeptember in 23-26, 2008 Bologna, Italy

Max-Planck-Institut fuer Radioastronomie E-mail: Tomoya Hirota Mizusawa VERA Observatory, NAOJ E-mail: Mareki Honma Mizusawa VERA Observatory, NAOJ E-mail: Hideyuki Kobayashi Mizusawa VERA Observatory, NAOJ E-mail: Yoon Kyung Choi Distance to VY Canis Majoris with VERA PoS(IX EVN Symposium)057 nd m massive alaxy. There , based on re- 4 IF channels mass function er, the distance od for distance ce, an accurate ugh their strong Yoon Kyung Choi ses – have large rations were made r evolution. Even 4], [18], [15]), and GHz observations, . Since SiO masers t of RSGs are very m a color-magnitude ril. We observed VY it digitization. During ucture and kinematics lution of the Universe, 024 Mbps, providing a itaka FX correlator [2], d massive evolved star. 059, simultaneously with O maser emission and the istance was obtained with ◦ 2 dependently. The flux den- ers enable us to study kine- y 1. transition, 22.235080 GHz) and SiO 23 -5 16 O masers are found further from the star, ob- 2 O 6 2 for maser emission. Details on observations and 2 1 − 0.2 km s O masers (H 2 ∼ 1 and 2 transitions, 43.122027 and 42.820584 GHz, respectively) arou = v 0, − 1 = J All data reduction was conducted using AIPS. Amplitude and bandpass calib The VERA observations of H Red supergiants (RSGs), massive evolved stars, are important in the evo Here, we describe distance measurements of VY CMa carried out with VERA In addition, VY CMa has been known as a good example to study mass loss fro VY Canis Majoris (VY CMa) is one of the most luminous red supergiants in our g for the maser source (VY CMa) and continuum source (J0725-2640) in correlation processing were described in [3]. masers (SiO remaining 15 IF channels weretwo allocated 16 to MHz the IF continuum channels source.were assigned were For to assigned the the to 43 continuum the source.yielding two The a correlation SiO velocity was transitions resolution done and of at the the M other 1 dual-beam [8]. The databandwidth were of recorded 256 onto MHz, subdivided magnetic into tapesthe 16 22 at IF GHz channels a observations, of rate one 16 16 of MHz, MHz 1 with IF 2-b channel was allocated to the H the red supergiant VY CMaCMa were and carried a out position for reference 13 source months J0725-2640 [12], since separated 2006 b Ap cently published paper [3], andof preliminary the results circumstellar on envelopes the around 3-dimensional VY CMa. str 2. Observations and Data Analysis Distance to VY Canis Majoris with VERA 1. Introduction servations of those masers wouldFurthermore, multi-epoch reveal phase-referencing the VLBI circumstellar observations of structurematics mas aroun of the circumstellar envelopes. evolved stars. VY CMa has strong maserare emission known in to its circumstellar be envelopes located at a few stellar radii and H are also several estimations for luminositythey and are temperature of based VY on CMa a (e.g., distanceassumption [1 that of the 1.5 distance kpc of [13]. VY CMaof This is the previously the NGC accepted same 2362 with d star that cluster ofdiagram. NGC was 2362. estimated with Howev Since an accuracy fundamental ofdistance 30 parameters determination % is of [11] essential. fro the star highly depend on its distan for example, they provide heavy elementsstellar into winds. the interstellar Since medium (ISM)(IMF) RSGs thro and are their extremely short rare lifetime,their due our fundamental to understanding properties is the – still steepnessuncertainty luminosities, poor of because temperatures, in of the massive ages, possible initial stella andfar, errors it initial in is mas the difficult to estimated obtainmeasurements. distances. trigonometric parallaxes, which Since is mos the most reliable meth PoS(IX EVN Symposium)057 ± 600 we used (J2000.0) = in VY CMa 500 δ 1 − sional Gaussian Yoon Kyung Choi in right ascension 400 1 ) was preformed at 32906, declination, respec- − evious estimate. As . arallax and a proper s [9]. After these cali- s with VERA. There- nsion and 0.68 mas in lay difference between 58 300 m 0.08 mas, corresponding DOY [day] details on possible causes 22 GHz with VERA, and r sources quantitatively in sitions. However, the op- flect that of the maser. We 22 re 1 shows the movements -2640) to the target source ± h 200 100 0 (J2000.0) = 07 ent the best annual parallax and linear proper 3 2 1 0 -1

2.5 1.5 0.5 -0.5 -1.5 α DEC offset[mas] DEC ce 2006 January 1). Points with error bars repre- 3 600 O maser spot at the LSR velocity of 0.55 km s 500 2 O maser spot at the LSR velocity of 0.55 km s 2 400 kpc using only the data in right ascension. Compared with the previ- 300 09 11 . . DOY [day] 0 0 − + 200 . In order to compare with theoretical evolutionary tracks on the HR diagram, 100 ⊙ The positions of the H L 5 0 10 2 1 0 -1 -2 1.5 0.5 -0.5 -1.5 -2.5

46’03".1410. With the newly determined distance, we re-estimated the luminosity of VY CMa to be (3 offset[mas] RA We measured positions of the H × ◦ 25 0.5) ously accepted distance [13], the distance of VY CMa became 76 % of the pr discussed in [4], [7], and [5],VLBI it astrometry. is difficult Therefore, to we estimate estimateddeclination the from errors individual the of erro standard 0.17 deviations of mas theof in least-square the analysis. right astrometric The asce errors are discussed in [3]. to a distance of 1.14 using J0725–2640 as a positionof reference source the over maser 13 spot months. astively. Figu Since a the function declination of data time havemotion, too (day we large of obtained errors a year) to trigonometric estimate in parallax an right annual of ascension p VY and CMa to be 0.88 − (left) and declination (right) againstsent time observed (day positions of of year the sin motion maser fit spot, model. and curves The repres position offsets are with respect to Figure 1: Distance to VY Canis Majoris with VERA sity of the reference sourcewas J0725-2640 expected was to measured be to 150 be mJyfore, 185 at mJy we 43 at applied GHz, fringe which fitting is(VY not solutions CMa) enough of for to the phase-referencing detect reference fringe atposite source 22 way (J0725 GHz of in application order using43 to phase GHz. get solutions We of absolute assumed the po that maser analso apparent source applied motion (VY the of CMa the dual-beam reference phase sourcethe calibration re two [8] beams, to and correct we instrumental finallybrations, de we calibrated obtained the synthesized tropospheric images zenith tofittings. delay measure offset the positions with two-dimen 3. Distance Measurements PoS(IX EVN Symposium)057 1 O = in − 2 1 J 0.16 − 2 3264, . ± s = v 58 0.9 km s O and SiO 3.24 m SiO masers 2 ± − olute motions, 0.9 km s 22 h etical track (see ± Yoon Kyung Choi 17.8 0 SiO masers (pink in right ascension − weak flux densities. − 1 e stellar surface, we than previous studies 17.8 1 ferent masers. While [16]. When we adopt − 0 K [15], our result is − ns of the H ⊙ = tions and velocities of H J 1 = annot make a final conclusion (J2000.0) = 07 v α 0.16 mas yr ± ter panel on (Y, Z) plane. X-, Y- and Z-axis 3.24 O masers from multi-epoch VERA obser- − 2 O masers represents a stellar traverse velocity. line of sight from the central star, respectively. 2 in declination, corresponding to 4 1 O maser features. The average motion is − 2 O masers (blue points), the O masers is 2 2 in declination at the distance of 1.14 kpc. The stellar radial 1 0.60 mas yr − ± 0 SiO masers (green points). The red arrows represent the abs 3.3 km s in declination, respectively. These correspond to − ± 1 1 − = at 1.14 kpc, respectively. (center) The 2-dimensional posi J 1 46’03".066. 2 − ◦ 0 SiO masers constrain the stellar position with a ring-like structure, the = 25 − v − 1 0.60 mas yr = 3.3 km s (left) The superposed map of the H J ± in right ascension and 2.06 ± 1 1 − = In addition, we obtained proper motions of the H As results of phase-referencing analyses, we obtained absolute positio 0 SiO masers only trace a part of the circumstellar envelope because of their v (J2000.0) = − Since SiO masers have been knownestimated to a be stellar located position in in thewith the closest circumstellar a region from envelopes high from th accuracy. the distribution of The the stellar position was estimated to be 1 The average of proper motions of the H vations. We assume that averaged motion of the H right ascension and 11.3 masers around VY CMa. Figurethe 2 (left) shows their distributions of three dif and 2.06 Figure 2: δ Distance to VY Canis Majoris with VERA temperature values from the literature. Whenconsistent with we the adopt theoretical a evolutionary temperature track of of 365 an initial mass of 25 M represent directions of right ascension, declination, and maser features projected on (X, Z) plane. (right) Same as cen 3000 K [18], the positionfigure on 4 the in [3]). HR However, diagram it is is([14], much [18]). still closer not Since to temperature the consistent does theoretically with not allowablewith the depend zone our on theor results. the distance, we c 4. Structure and Kinematics of the Circumstellar Envelopes and 11.3 which the average motion was subtracted, of the H points), and the mas yr PoS(IX EVN Symposium)057 O 2 ing other eature with velopes around celestial sphere Yoon Kyung Choi revious observational ow the 3-dimensional we still cannot explain ipolar outflow of VY CMa 2 (left)). mmunity’s sixth Framework 004, ApJ, 616L, 47 3 33, 2716 74, 733 bayashi, M. Inoue, & H. Kobayashi (Tokyo: 07, AJ, 133, 1236 , and Hallan, K. L. 1961, Lowell Obs. Bull., 5, 5 [1]. After the average motion was subtracted, the H 1 − O masers on projected 2-dimensional planes from our results. 2 0) emission with VLA [17], VY CMa shows a bipolar outflow along − 1 = J 0 = v O maser features, we estimated positions along the line of sight of each maser f 2 Universal Academy Press), 79 133 We consider the 3-dimensional structure and kinematics of the circumstellar en [3] Choi, Y. K., et al. 2008, PASJ,[4] 60, 1007 Hachisuka, K. et al. 2006, ApJ,[5] 645, 337 Hirota, T. et al. 2007, PASJ, 59,[6] 897 Hirota, T. et al. 2008, PASJ, 60,[7] 37 Honma, M. et al. 2007, PASJ,[8] 59, 889 Honma, M. et al. 2008, PASJ,[9] 60, 935 Honma, M., Tamura, R., & Reid, M. J. 2008, PASJ, 60, 951 [2] Chikada, Y., et al. 1991, in Frontiers of VLBI, ed. H. Hira [1] Bowers, P. F., Johnston, K. J. & Spencer, J. H. 1983, ApJ, 2 [12] Kovalev, Y. Y., Petrov, L., Fomalont, E., &[13] Gordon, D. Lada, 20 C. J., & Reid, M.[14] J. 1978, Le ApJ, Sidaner, 219, P., 95 & Le Bertre, T.[15] 1996, A&A, Massey, 314, P., Leveque, 896 E. M., & Plez, B. 2006, ApJ, 646, 120 [11] Johnson, H. L., Hoag, A. A., Iriarte, B., Mitchell, R. I. [16] Meynet, G., & Maeder, A. 2003,[17] A&A, 404, Shinnaga, 975 H., Moran, J. M., Young, K. H., and Ho, P. T. P. 2 [10] Humphreys, R. M., Helton, L.A., & Jones, T. J. 2007, AJ, 1 the line of sight. Although we need a more complicated 3-dimensional model includ parameters, for example acceleration, our preliminary resultsalong suggest the a line b of sight, andasymmetric it expansion is observed consistent with with HST results in from larger [17]. scale [10]. However, Acknowledgment This work has benefited from researchProgramme funding under from RadioNet the R113CT European 2003 Co 5058187. References It clearly shows elongated structure along the line of sight. According to a p result of SiO ( respect to the central star assuming astructure simple radial and outflow kinematics model. of Figure 2 the sh H masers show a tendency of expansion from the central star (see figure VY CMa. With the 3-dimensional velocities andof the the 2-dimensional H positions on the Distance to VY Canis Majoris with VERA velocity was adopted to be 21.1 km s PoS(IX EVN Symposium)057 Yoon Kyung Choi chuster, M. T., & Krautter, J. 2001, ApJ, 6 121, 1111 Distance to VY Canis Majoris with VERA [18] Smith, N., Humphreys, R. M., Davidson, K., Gehrz, R. D. S