JVN observations of H2O masers around the evolved star IRAS 22480+6002

We report on the H2O maser distributions around IRAS 22480+6002 (=IRC+60370) observed with the Japanese VLBI Network (JVN) at three epochs spanning 2 months. This object was identified as a K-type supergiant in 1970s, which was unusual as a stellar maser source. The spectrum of H2O masers consists of 5 peaks separated roughly equally by a few km/s each. The H2O masers were spatially resolved into more than 15 features, which spread about 50 mas along the east--west direction. However, no correlation was found between the proper motion vectors and their spatial distributions; the velocity field of the envelope seems random. A statistical parallax method applied to the observed proper-motion data set gives a distance of 1.0+-0.4 kpc for this object, that is considerably smaller than previously thought. The distance indicates that this is an evolved star with L~5800 Lsun. This star shows radio, infrared, and optical characteristics quite similar to those of the population II post-AGB stars such as RV Tau variables.Comment: 7 pages, 5 figures, PASJ 60, No. 1 (2008 Feb. 25 issue) in press. High res. figures available at ftp://ftp.nro.nao.ac.jp/nroreport/no657.pdf.g

A collimated jet and an infalling-rotating disk in G192.16-3.84 traced by H2O maser emission

We report H2O masers associated with the massive-star forming region G192.16-3.84 observed with the new Japan VLBI network at three epochs spanned for two months, which have revealed the three-dimensional kinematical structure of the whole \h2o maser region in G192.16-3.84, containing two young stellar objects separated by ~1200 AU. The maser spatio-kinematical structure has well persisted since previous observations, in which the masers are expected to be associated with a highly-collimated bipolar jet and an infalling-rotating disk in the northern and southern clusters of H2O maser features, respectively. We estimated a jet expansion speed of ~100 km/s and re-estimated a dynamical age of the whole jet to be 5.6x10^4 yrs. We have investigated the spatial distribution of Doppler velocities during the previous and present observations and relative proper motions of H2O maser features in the southern cluster, and a relative bulk motion between the two maser clusters. They are well explained by a model of an infalling-rotating disk with a radius of ~1000 AU and a central stellar mass of 5-10 M_sun, rather than by a model of a bipolar jet perpendicular to the observed CO outflow. Based on the derived H2O maser spatio-kinematical parameters, we discuss the formation mechanism of the massive young stellar objects and the outflow development in G192.16-3.84.Comment: 30 pages, 3 figures, 3 tables, to be published in the Publication of the Astronomical Society of Japan issued on 2006 October 2

Discovery of superhumps during a normal outburst of SU Ursae Majoris

We report on time-resolved photometry during a 2012 January normaloutburst of SU UMa. The light curve shows hump-like modulations with a period of 0.07903(11) d, which coincides with the known superhump period of SU UMa during superoutbursts. We interpret this as superhump, based on the observed periodicity, profiles of the averaged light curve, and the $g'-I_{\rm c}$ variation during the normal outburst. This is the first case that superhumps are detected during an isolated normal outburst of SU UMa-type dwarf novae. The present result strongly suggests that the radius of the accretion disk already reaches the 3:1 resonance even in the midst of the supercycle.Comment: 4 pages, 4 figure, PASJ letter in pres

Astrometry of Galactic Star-Forming Region G48.61+0.02 with VERA

We performed the astrometry of H2O masers in the Galactic star-forming region G48.61+0.02 with the VLBI Exploration of Radio Astrometry (VERA). We derived a trigonometric parallax of 199+/-7 micro as, which corresponds to a distance of 5.03+/-0.19 kpc. The distance to G48.61+0.02 is about a half of its far kinematic distance, which was often assumed previously. This distance places G48.61+0.02 in the Sagittarius-Carina arm and near the active star forming region and the supernova remnant W51. We also obtained the three dimensional motion of G48.61+0.02, and found that it has a large peculiar motion of 40+/-5 km/s. This peculiar motion would be originated with the multiple supernovae explosions in W51, or the streaming motion across the Sagittarius-Carina arm.Comment: 8 pages, 5 figures, accepted for PASJ (Vol. 63 No. 4

NH3 in the Galactic Center is formed in Cool Conditions

It is an open question why the temperature of molecular gas in the Galactic center region is higher than that of dust. To address this problem, we made simultaneous observations in the NH_3 (J,K) = (1,1), (2,2), and (3,3) lines of the central molecular zone (CMZ) using the Kagoshima 6 m telescope. The ortho-to-para ratio of NH_3 molecules in the CMZ is 1.5--3.5 at most observed area. This ratio is higher than the statistical equilibrium value, and suggests that the formation temperature of NH_3 is 11--20 K. This temperature is similar to the dust temperature estimated from the submillimeter and infrared continuum. This result suggests that the NH_3 molecules in the CMZ were produced on dust grains with the currently observed temperature (11--20 K), and they were released into the gas phase by supernova shocks or collisions of dust particles. The discrepancy between warm molecular gas and cold dust can be explained by the transient heating of the interstellar media in the CMZ approximately 10^5 years ago when the NH_3 molecules were released from the dust.Comment: 19 pages, 12 figures, accepted for PAS

Propagation of Highly Efficient Star Formation in NGC 7000

We surveyed the (1,1), (2,2), and (3,3) lines of NH3 and the H2O maser toward the molecular cloud L935 in the extended HII region NGC 7000 with an angular resolution of 1.6' using the Kashima 34-m telescope. We found five clumps in the NH3 emission with a size of 0.2--1 pc and mass of 9--452 M_sun. The molecular gas in these clumps has a similar gas kinetic temperature of 11--15 K and a line width of 1--2 km/s. However, they have different star formation activities such as the concentration of T-Tauri type stars and the association of H2O maser sources. We found that these star formation activities are related to the geometry of the HII region. The clump associated with the T-Tauri type star cluster has a high star formation efficiency of 36--62%. This clump is located near the boundary of the HII region and molecular cloud. Therefore, we suggest that the star formation efficiency increases because of the triggered star formation.Comment: 19 pages, 15 figures, accepted for PASJ Vol.63 No.

H2O maser motions and the distance of the star forming region G192.16-3.84

We present the results of astrometic observations of H2O masers associated with the star forming region G192.16-3.84 with the VLBI Exploration of Radio Astrometry (VERA). The H2O masers seem to be associated with two young stellar objects (YSOs) separated by \sim1200 AU as reported in previous observations. In the present observations, we successfully detected an annual parallax of 0.66 \pm 0.04 mas for the H2 O masers, which corresponds to a distance to G192.16-3.84 of D = 1.52 \pm 0.08 kpc from the Sun. The determined distance is shorter than the estimated kinematic distance. Using the annual parallax distance and the estimated parameters of the millimeter continuum emission, we estimate the mass of the disk plus circumstellar cloud in the southern young stellar object to be 10.0+4.3M\cdot. We also estimate the galactocentric distance and the peculiar motion -3.6 of G192.16-3.84, relative to a circular Galactic rotation: R\star = 9.99 \pm 0.08 kpc, Z\star = -0.10 \pm 0.01 kpc, and (U\star,V\star,W\star)=(-2.8\pm1.0,-10.5\pm0.3,4.9\pm2.7)[kms-1]respectively. The peculiar motion of G192.16-3.84 is within that typically found in recent VLBI astrometric results. The angular distribution and three-dimensional velocity field of H2O maser features associated with the northern YSO indicate the existence of a bipolar outflow with a major axis along the northeast-southwest direction.Comment: 9 pages, 2 figures and 4 tables. Accepted for publication on PAS

A Complete Survey of the Central Molecular Zone in NH3

We present a map of the major part of the central molecular zone (CMZ) of simultaneous observations in the NH3 (J,K) = (1,1) and (2,2) lines using the Kagoshima 6-m telescope. The mapped area is -1.000 < l < 1.625 deg, -0.375 < b < +0.250 deg. The kinetic temperatures derived from the (2,2) to (1,1) intensity ratios are 20--80 K or exceed 80 K. The gases corresponding to temperature of 20--80 K and > 80 K contain 75% and 25% of the total NH3 flux, respectively. These temperatures indicate that the dense molecular gas in the CMZ is dominated by gas that is warmer than the majority of the dust present there. A comparison with the CO survey by Sawada et al. (2001) shows that the NH3 emitting region is surrounded by a high pressure region on the l-v plane. Although NH3 emission traces dense gas, it is not extended into a high pressure region. Therefore, the high pressure region is less dense and has to be hotter. This indicates that the molecular cloud complex in the Galactic center region has a ``core'' of dense and warm clouds which are traced by the NH3 emission, and an ``envelope'' of less dense and hotter gas clouds. Besides heating by ambipolar diffusion, the hot plasma gas emitting the X-ray emission may heat the hot ``envelope''.Comment: 21 pages, 14 figures, accepted for PAS