arXiv subjects

Naoko Matsumoto

Publications and source records attributed to Naoko Matsumoto.

28 records · Page 2Linked to original sources

arXiv2013

Observations of 6.7 GHz Methanol Masers with EAVN I: VLBI Images of the first Epoch of Observations

Very long baseline interferometry (VLBI) monitoring of the 6.7 GHz methanol maser allows us to measure the internal proper motions of the maser spots and therefore study the gas motion around high-mass young stellar objects. To this end, we have begun monitoring observations with the East-Asian VLBI Network. In this paper we present the results of the first epoch observation for 36 sources, including 35 VLBI images of the methanol maser. Since two independent sources were found in three images, respectively, images of 38 sources were obtained. In 34 sources, more than or equal to 10 spots were detected. The observed spatial scale of the maser distribution was from 9 to 4900 astronomical units, and the following morphological categories were observed: elliptical, arched, linear, paired, and complex. The position of the maser spot was determined to an accuracy of approximately 0.1 mas, sufficiently high to measure the internal proper motion from two years of monitoring observations. The VLBI observation, however, detected only approximately 20% of all maser emission, suggesting that the remaining 80% of the total flux was spread into an undetectable extended distribution. Therefore, in addition to high-resolution observations, it is important to observe the whole structure of the maser emission including extended low-brightness structures, to reveal the associated site of the maser and gas motion.

astro-ph.SR↗

arXiv2012

Fundamental Parameters of the Milky Way Galaxy Based on VLBI astrometry

We present analyses to determine the fundamental parameters of the Galaxy based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA and EVN. We model the Galaxy's structure with a set of parameters including the Galaxy center distance R_0, the angular rotation velocity at the LSR Omega_0, mean peculiar motion of the sources with respect to Galactic rotation (U_src, V_src, W_src), rotation-curve shape index, and the V component of the Solar peculiar motions V_sun. Based on a Markov chain Monte Carlo method, we find that the Galaxy center distance is constrained at a 5% level to be R_0 = 8.05 +/- 0.45 kpc, where the error bar includes both statistical and systematic errors. We also find that the two components of the source peculiar motion U_src and W_src are fairly small compared to the Galactic rotation velocity, being U_src = 1.0 +/- 1.5 km/s and W_src = -1.4 +/- 1.2 km/s. Also, the rotation curve shape is found to be basically flat between Galacto-centric radii of 4 and 13 kpc. On the other hand, we find a linear relation between V_src and V_sun as V_src = V_sun -19 (+/- 2) km/s, suggesting that the value of V_src is fully dependent on the adopted value of V_sun. Regarding the rotation speed in the vicinity of the Sun, we also find a strong correlation between Omega_0 and V_sun. We find that the angular velocity of the Sun, Omega_sun, which is defined as Omega_sun = Omega_0 + V_sun/R_0, can be well constrained with the best estimate of Omega_sun = 31.09 +/- 0.78 km/s/kpc. This corresponds to Theta_0 = 238 +/- 14 km/s if one adopts the above value of R_0 and recent determination of V_sun ~ 12 km/s.

astro-ph.GA↗

arXiv2012

Pilot VLBI Survey of SiO v=3 J=1--0 Maser Emission around Evolved Stars

In this Letter, we report detections of SiO v=3 J=1--0 maser emission in very long baseline interferometric (VLBI) observations towards 4 out of 12 long-period variable stars: WX Psc, R Leo, W Hya, and T Cep. The detections towards WX Psc and T Cep are new ones. We also present successful astrometric observations of SiO v=2 and v=3 J=1--0 maser emissions associated with two stars: WX Psc and W Hya and their position-reference continuum sources: J010746.0+131205 and J135146.8-291218 with the VLBI Exploration of Radio Astrometry (VERA). The relative coordinates of the position-reference continuum source and SiO v=3 maser spots were measured with respect to those of an SiO v=2 maser spot adopted as fringe-phase reference. Thus the faint continuum sources were inversely phase-referenced to the bright maser sources. It implies possible registration of multiple SiO maser line maps onto a common coordinate system with 10 microarcsecond-level accuracy.

astro-ph.SR↗

arXiv2010

VLBI Monitoring of 3C 84 (NGC 1275) in Early Phase of the 2005 Outburst

Multi-epoch Very Long Baseline Interferometry (VLBI) study of the sub-pc scale jet of 3C 84 is presented. We carried out 14-epoch VLBI observations during 2006-2009 with the Japanese VLBI Network (JVN) and the VLBI Exploration of Radio Astrometry (VERA), immediately following the radio outburst that began in 2005. We confirmed that the outburst was associated with the central ~1 pc core, accompanying the emergence of a new component. This is striking evidence of the recurrence of jet activity. The new component became brighter during 2008, in contrast to the constant gamma-ray emission that was observed with the Fermi Gamma-ray Space Telescope during the same time. We found that the projected speed of the new component is 0.23c from 2007/297 (2007 October 24) to 2009/114 (2009 April 24). The direction of movement of this component differs from that of the pre-existing component by ~40 degree. This is the first measurement of kinematics of a sub-pc jet in a gamma-ray active phase. Possible detection of jet deceleration and the jet kinematics in connection with the gamma-ray emission is discussed.

astro-ph.HE↗

arXiv2008

VLBI Astrometry of AGB Variables with VERA -- A Semiregular Variable S Crateris --

We present a distance measurement for the semiregular variable S Crateris (S Crt) based on its annual parallax. With the unique dual beam system of the VLBI Exploration for Radio Astrometry (VERA) telescopes, we measured the absolute proper motion of a water maser spot associated with S Crt, referred to the quasar J1147-0724 located at an angular separation of 1.23$^{\circ}$. In observations spanning nearly two years, we have detected the maser spot at the LSR velocity of 34.7 km s$^{-1}$, for which we measured the annual parallax of 2.33$\pm$0.13 mas corresponding to a distance of 430$^{+25}_{-23}$ pc. This measurement has an accuracy one order of magnitude better than the parallax measurements of HIPPARCOS. The angular distribution and three-dimensional velocity field of maser spots indicate a bipolar outflow with the flow axis along northeast-southwest direction. Using the distance and photospheric temperature, we estimate the stellar radius of S Crt and compare it with those of Mira variables.

astro-ph↗

arXiv2008

Distance to VY Canis Majoris with VERA

We report astrometric observations of H2O masers around the red supergiant VY Canis Majoris (VY CMa) carried out with VLBI Exploration of Radio Astrometry (VERA). Based on astrometric monitoring for 13 months, we successfully measured a trigonometric parallax of 0.88 +/- 0.08 mas, corresponding to a distance of 1.14 +0.11/-0.09 kpc. This is the most accurate distance to VY CMa and the first one based on an annual parallax measurement. The luminosity of VY CMa has been overestimated due to a previously accepted distance. With our result, we re-estimate the luminosity of VY CMa to be (3 +/- 0.5) x 10^5 L_sun using the bolometric flux integrated over optical and IR wavelengths. This improved luminosity value makes location of VY CMa on the Hertzsprung-Russel (HR) diagram much closer to the theoretically allowable zone (i.e. the left side of the Hayashi track) than previous ones, though uncertainty in the effective temperature of the stellar surface still does not permit us to make a final conclusion.

astro-ph↗

arXiv2008

Astrometry of H$_{2}$O Masers in Nearby Star-Forming Regions with VERA. III. IRAS 22198+6336 in L1204G

We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H$_{2}$O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud L1204G. Based on the phase-referencing VLBI astrometry, we derive an annual parallax of IRAS 22198+6336 to be 1.309$\pm$0.047 mas, corresponding to the distance of 764$\pm$27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduce the errors in the derived annual parallax by employing the position measurements for all of the 26 detected maser spots. Based on this result, we reanalyze the spectral energy distribution (SED) of IRAS 22198+6336 and find that the bolometric luminosity and total mass of IRAS 22198+6336 are 450$L_{\odot}$ and 7$M_{\odot}$, respectively. These values are consistent with an intermediate-mass YSO deeply embedded in the dense dust core, which has been proposed to be an intermediate-mass counterpart of a low-mass Class 0 source. In addition, we obtain absolute proper motions of the H$_{2}$O masers for the most blue-shifted components. We propose that the collimated jets aligned along the east-west direction are the most plausible explanation for the origin of the detected maser features.

astro-ph↗

arXiv2008

Distance to NGC 281 in a Galactic Fragmenting Superbubble: Parallax Measurements with VERA

We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H2O maser source in the Galactic star-forming region NGC 281 West, which has been considered to be part of a 300-pc superbubble. We successfully detected a trigonometric parallax of 0.355+/-0.030 mas, corresponding to a source distance of 2.82+/-0.24 kpc. Our direct distance determination of NGC 281 has resolved the large distance discrepancy between previous photometric and kinematic studies; likely NGC 281 is in the far side of the Perseus spiral arm. The source distance as well as the absolute proper motions were used to demonstrate the 3D structure and expansion of the NGC 281 superbubble, ~650 pc in size parallel to the Galactic disk and with a shape slightly elongated along the disk or spherical, but not vertically elongated, indicating the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as ~20 km/s both perpendicular to and parallel to the Galactic disk with a consistent timescale of ~20 Myr.

astro-ph↗

arXiv2007

Distance to Orion KL Measured with VERA

We present the initial results of multi-epoch VLBI observations of the 22 GHz H2O masers in the Orion KL region with VERA (VLBI Exploration of Radio Astrometry). With the VERA dual-beam receiving system, we have carried out phase-referencing VLBI astrometry and successfully detected an annual parallax of Orion KL to be 2.29+/-0.10 mas, corresponding to the distance of 437+/-19 pc from the Sun. The distance to Orion KL is determined for the first time with the annual parallax method in these observations. Although this value is consistent with that of the previously reported, 480+/-80 pc, which is estimated from the statistical parallax method using proper motions and radial velocities of the H2O maser features, our new results provide the much more accurate value with an uncertainty of only 4%. In addition to the annual parallax, we have detected an absolute proper motion of the maser feature, suggesting an outflow motion powered by the radio source I along with the systematic motion of source I itself.

astro-ph↗

arXiv2007

Absolute Proper Motions of H2O Masers Away from the Galactic Plane Measured with VERA in the "Superbubble" Region NGC 281

We report on absolute proper-motion measurements of an H2O maser source in the NGC 281 West molecular cloud, which is located ~320 pc above the Galactic plane and is associated with an HI loop extending from the Galactic plane. We have conducted multi-epoch phase-referencing observations of the maser source with VERA (VLBI Exploration of Radio Astrometry) over a monitoring period of 6 months since May 2006. We find that the H2O maser features in NGC 281 West are systematically moving toward the southwest and further away from the Galactic plane with a vertical velocity of ~20-30 km/s at its estimated distance of 2.2-3.5 kpc. Our new results provide the most direct evidence that the gas in the NGC 281 region on the HI loop was blown out from the Galactic plane, most likely in a superbubble driven by multiple or sequential supernova explosions in the Galactic plane.

astro-ph↗