arXiv subjects

Ken'ichi Tatematsu

Publications and source records attributed to Ken'ichi Tatematsu.

At least 109 records · Page 6Linked to original sources

arXiv2014

Dense Molecular Clumps associated with the LMC Supergiant Shells LMC 4 \& LMC 5

We investigate the effects of Supergiant Shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. $^{12}$CO ($J$=3-2, 1-0) and $^{13}$CO ($J$=1-0) observations with the ASTE and Mopra telescopes have been carried out towards these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities ($n({\rm H}_2)$) of the clumps are distributed from low to high density ($10^3$-$10^5$ cm$^{-3}$) and their kinetic temperatures ($T_{\rm kin}$) are typically high (greater than $50$ K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of H$α$, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density HI envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high $n({\rm H}_2)$ and $T_{\rm kin}$, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

astro-ph.GA↗

arXiv2014

Thermal Starless Ammonia Core Surrounded by CCS in the Orion A Cloud

We imaged two starless molecular cloud cores, TUKH083 and TUKH122, in the Orion A giant molecular cloud in the CCS and ammonia (NH$_3$) emission with the Very Large Array. TUKH122 contains one NH$_3$ core "TUKH122-n," which is elongated and has a smooth oval boundary. Where observed, the CCS emission surrounds the NH$_3$ core. This configuration resembles that of the N$_2$H$^+$ and CCS distribution in the Taurus starless core L1544, a well-studied example of a dense prestellar core exhibiting infall motions. The linewidth of TUKH122-n is narrow (0.20 km s$^{-1}$) in the NH$_3$ emission line and therefore dominated by thermal motions. The smooth oval shape of the core boundary and narrow linewidth in NH$_3$ seem to imply that TUKH122-n is dynamically relaxed and quiescent. TUKH122-n is similar to L1544 in the kinetic temperature (10 K), linear size (0.03 pc), and virial mass ($\sim$ 2 $M_{\odot}$). Our results strongly suggest that TUKH122-n is on the verge of star formation. TUKH122-n is embedded in the 0.2 pc massive (virial mass $\sim$ 30 $M_{\odot}$) turbulent parent core, while the L1544 NH$_3$ core is embedded in the 0.2 pc less-massive (virial mass $\sim$ 10 $M_{\odot}$) thermal parent core. TUKH083 shows complicated distribution in NH$_3$, but was not detected in CCS. The CCS emission toward TUKH083 appears to be extended, and is resolved out in our interferometric observations.

astro-ph.GA↗

arXiv2014

X-ray Spectroscopy of the Mixed Morphology Supernova Remnant W28 with XMM-Newton

We report on spatially resolved X-ray spectroscopy of the north-eastern part of the mixed morphology supernova remnant (SNR) W28 with {\it XMM-Newton}. The observed field of view includes a prominent and twisted shell emission forming the edge of this SNR as well as part of the center-filled X-ray emission brightening toward the south-west edge of the field of view. The shell region spectra are in general represented by an optically thin thermal plasma emission in collisional ionization equilibrium with a temperature of $\sim$0.3~keV and a density of $\sim$10~cm$^{-3}$, which is much higher than the density obtained for inner parts. In contrast, we detected no significant X-ray flux from one of the TeV $γ$-ray peaks with an upper-limit flux of 2.1$\times$10$^{-14}$ erg cm$^{-2}$ s$^{-1}$ in the 2--10~keV band. The large flux ratio of TeV to X-ray, larger than 16, and the spatial coincidence of the molecular cloud and the TeV $γ$-ray emission site indicate that the TeV $γ$-ray of W28 is $π^{0}$-decay emission originating from collisions between accelerated protons and molecular cloud protons. Comparing the spectrum in the TeV band and the X-ray upper limit, we obtained a weak upper limit on the magnetic field strength $B\lesssim$ 1500~$μ$G.

astro-ph.HE↗

arXiv2013

Chemical Variation in Molecular Cloud Cores in the Orion A Cloud. II

We have mapped six molecular cloud cores in the Orion A giant molecular cloud (GMC), whose kinetic temperatures range from 10 to 30 K, in CCS and N2H+ with Nobeyama 45 m radio telescope to study their chemical characteristics. We identified 31 intensity peaks in the CCS and N2H+ emission in these molecular cloud cores. It is found for cores with temperatures lower than ~ 25 K that the column density ratio of N(N2H+)/N(CCS) is low toward starless core regions while it is high toward star-forming core regions, in case that we detected both of the CCS and N2H+ emission. This is very similar to the tendency found in dark clouds (kinetic temperature ~ 10 K). The criterion found in the Orion A GMC is N(N2H+)/N(CCS) ~ 2-3. In some cases, the CCS emission is detected toward protostars as well as the N2H+ emission. Secondary late-stage CCS peak in the chemical evolution caused by CO depletion may be a possible explanation for this. We found that the chemical variation of CCS and N2H+ can also be used as a tracer of evolution in warm (10-25 K) GMC cores. On the other hand, some protostars do not accompany N2H+ intensity peaks but are associated with dust continuum emitting regions, suggesting that the N2H+ abundance might be decreased due to CO evaporation in warmer star-forming sites.

astro-ph.GA↗

arXiv2011

Evidence for Inflow in High-Mass Star-Forming Clumps

We analyze the HCO+ 3-2 and H13CO+ 3-2 line profiles of 27 high-mass star-forming regions to identify asymmetries that are suggestive of mass inflow. Three quantitative measures of line asymmetry are used to indicate whether a line profile is blue, red or neither - the ratio of the temperature of the blue and red peaks, the line skew and the dimensionless parameter delta_v. We find nine HCO+ 3-2 line profiles with a significant blue asymmetry and four with significant red asymmetric profiles. Comparing our HCO+ 3-2 results to HCN 3-2 observations from Wu et al. (2003, 2010), we find that eight of the blue and three of red have profiles with the same asymmetry in HCN. The eight sources with blue asymmetries in both tracers are considered strong candidates for inflow. Quantitative measures of the asymmetry (e.g. delta_v) tend to be larger for HCN. This, combined with possible HCO+ abundance enhancements in outflows, suggests that HCN may be a better tracer of inflow. Understanding the behavior of common molecular tracers like HCO+ in clumps of different masses is important for properly analyzing the line profiles seen in a sample of sources representing a broad range of clump masses. Such studies will soon be possible with the large number of sources with possible self-absorption seen in spectroscopic follow-up observations of clumps identified in the Bolocam Galactic Plane Survey.

astro-ph.SR↗

arXiv2011

Radio Imaging of the NGC 1333 IRAS 4A Region: Envelope, Disks, and Outflows of a Protostellar Binary System

The NGC 1333 IRAS 4A protobinary was observed in the 1.3 cm and 6.9 mm continuum and the ammonia and SiO lines, with an angular resolution of about 0.4 arcseconds. The continuum maps show the circumstellar structures of the two protostars, A1 and A2. The A1 system is brighter and more massive than the A2 system. The ratio of mass, including dense gas and protostar, is about 6. The properties of the circumstellar disks and outflows suggest that A1 may be younger than A2. The deflected part of the northeastern jet of A2 is bright in the SiO line, and the distance between the brightest peak and deflection point suggests that the enhancement of SiO takes about 100 yr after the collision with a dense core. The ammonia maps show a small structure that seems to be a part of the obstructing core. The outflow properties were studied by comparing interferometric maps of SiO, ammonia, formaldehyde, and HCN lines. Their overall structures agree well, suggesting that these species are excited by the same mechanism. However, the intensity distributions show that SiO is chemically unique. SiO may be directly linked to the primary jet while the other species may be tracing the entrained ambient gas.

astro-ph.GA↗

arXiv2011

The Physical Properties of High-Mass Star-Forming Clumps: A Systematic Comparison of Molecular Tracers

We present observations of HCO+ and H^13CO+, N2H+, HCS+, HCN and HN^13C, SO and ^34SO, CCH, SO_2, and CH_3OH-E towards a sample of 27 high-mass clumps coincident with water maser emission. All transitions are observed with or convolved to nearly identical resolution (30"), allowing for inter-comparison of the clump properties derived from the mapped transitions. We find N2H+ emission is spatially differentiated compared to the dust and the other molecules towards a few very luminous cores (10 of 27) and the N2H+ integrated intensity does not correlate well with dust continuum flux. We calculate the effective excitation density, n_eff, the density required to excite a 1 K line in T_kin=20 K gas for each molecular tracer. The intensity of molecular tracers with larger effective excitation densities (n_eff > 10^5 cm^-3) appear to correlate more strongly with the submillimeter dust continuum intensity. The median sizes of the clumps are anti-correlated with the n_eff of the tracers (which span more than three orders of magnitude). Virial mass is not correlated with n_eff, especially where the lines are optically thick as the linewidths may be broadened significantly by non-virial motions. The median mass surface density and median volume density of the clumps is correlated with n_eff indicating the importance of understanding the excitation conditions of the molecular tracer when deriving the average properties of an ensemble of cores.

astro-ph.GA↗

arXiv2011

Rotation of the NGC 1333 IRAS 4A2 Protostellar Jet

The bipolar jet of the NGC 1333 IRAS 4A2 protostar shows a velocity gradient in the direction perpendicular to the jet axis. This lateral velocity gradient can be seen throughout the jet imaged in a silicon monoxide line, 2500-8700 AU from the driving source, and is consistent with the rotation of the accretion disk. If this gradient is caused by the rotation of the jet around its axis, the average specific angular momentum is about 1.5 x 10^21 cm^2 s^-1. Comparison of the kinematics between the jet and the disk suggests that the jet-launching region on the disk has a radius of about 2 AU, which supports the disk-wind models. The angular momentum transported away by the jet seems to be large enough for the protostar to accrete matter from the disk, confirming the crucial role of jets in the early phase of star formation process.

astro-ph.GA↗

arXiv2010

Dense Clumps in Giant Molecular Clouds in the Large Magellanic Cloud: Density and Temperature Derived from $^{13}$CO($J=3-2$) Observations

In order to precisely determine temperature and density of molecular gas in the Large Magellanic Cloud, we made observations of optically thin $^{13}$CO($J=3-2$) transition by using the ASTE 10m telescope toward 9 peaks where $^{12}$CO($J=3-2$) clumps were previously detected with the same telescope. The molecular clumps include those in giant molecular cloud (GMC) Types I (with no signs of massive star formation), II (with HII regions only), and III (with HII regions and young star clusters). We detected $^{13}$CO($J=3-2$) emission toward all the peaks and found that their intensities are 3 -- 12 times lower than those of $^{12}$CO($J=3-2$). We determined the intensity ratios of $^{12}$CO($J=3-2$) to $^{13}$CO($J=3-2$), $R^{12/13}_{3-2}$, and $^{13}$CO($J=3-2$) to $^{13}$CO($J=1-0$), $R^{13}_{3-2/1-0}$, at 45$\arcsec$ resolution. These ratios were used for radiative transfer calculations in order to estimate temperature and density of the clumps. The parameters of these clumps range kinetic temperature $T\mathrm{_{kin}}$ = 15 -- 200 K, and molecular hydrogen gas density $n(\mathrm{H_2})$ = 8$\times 10^2$ -- 7$\times 10^3$ cm$^{-3}$. We confirmed that the higher density clumps show higher kinetic temperature and that the lower density clumps lower kinetic temperature at a better accuracy than in the previous work. The kinetic temperature and density increase generally from a Type I GMC to a Type III GMC. We interpret that this difference reflects an evolutionary trend of star formation in molecular clumps. The $R^{13}_{3-2/1-0}$ and kinetic temperature of the clumps are well correlated with H$α$ flux, suggesting that the heating of molecular gas $n(\mathrm{H_2})$ = $10^3$ -- $10^4$ cm$^{-3}$ can be explained by stellar FUV photons.

astro-ph.GA↗

arXiv2010

Chemical Variation in Molecular Cloud Cores in the Orion A Cloud

We have observed molecular cloud cores in the Orion A giant molecular cloud (GMC) in CCS, HC3N, DNC, and HN13C to study their chemical characteristics. We have detected CCS in the Orion A GMC for the first time. CCS was detected in about a third of the observed cores. The cores detected in CCS are not localized but are widely distributed over the Orion A GMC. The CCS peak intensity of the core tends to be high in the southern region of the Orion A GMC. The HC3N peak intensity of the core also tends to be high in the southern region, while there are HC3N intense cores near Orion KL, which is not seen in CCS. The core associated with Orion KL shows broad HC3N line profile, and star formation activity near Orion KL seems to enhance the HC3N emission. The column density ratio of NH3 to CCS is lower near the middle of the filament, and is higher toward the northern and southern regions along the Orion A GMC filament. This ratio is known to trace the chemical evolution in nearby dark cloud cores, but seems to be affected by core gas temperature in the Orion A GMC: cores with low NH3 to CCS column density ratios tend to have warmer gas temperature. The value of the column density ratio of DNC to HN13C is generally similar to that in dark cloud cores, but becomes lower around Orion KL due to higher gas temperature.

astro-ph.GA↗

arXiv2010

Kinematics of the Ammonia Disk around the Protostar NGC 1333 IRAS 4A2

The NGC 1333 IRAS 4A protobinary was observed in the ammonia (2, 2) and (3, 3) lines with an angular resolution of 0.3 arcsec. The ammonia emission source of IRAS 4A2 is elongated in the direction perpendicular to the bipolar jet and has a size of 0.55 arcsec or 130 AU. This emission structure was interpreted as a circumstellar disk around the IRAS 4A2 protostar, and the rotation kinematics of the disk was investigated by making a position-velocity diagram along the major axis. Assuming a Keplerian rotation, the disk has a rotation velocity of 1.8 km/s at a radius of 20 AU, which implies a central object of about 0.08 solar masses. The collapse age of the protostar is about 50,000 yr. The mass, accretion rate, and age are consistent with what are expected from the standard theory of low-mass star formation. If IRAS 4A2 grows at this rate, it may become a star similar to the Sun.

astro-ph.GA↗

arXiv2009

Warm and Dense Molecular Gas in the N159 Region: 12CO J=4-3 and 13CO J=3-2 Observations with NANTEN2 and ASTE

New 12CO J=4-3 and 13CO J=3-2 observations of the N159 region in the Large Magellanic Cloud have been made. The 12CO J=4-3 distribution is separated into three clumps. These new measurements toward the three clumps are used in coupled calculations of molecular rotational excitation and line radiation transfer, along with other transitions of the 12CO as well as the isotope transitions of 13CO. The temperatures and densities are determined to be ~70-80K and ~3x10^3 cm-3 in N159W and N159E and ~30K and ~1.6x10^3 cm-3 in N159S. These results are compared with the star formation activity. The N159E clump is associated with embedded cluster(s) as observed at 24 micron and the derived high temperature is explained as due to the heating by these sources. The N159E clump is likely responsible for a dark lane in a large HII region by the dust extinction. The N159W clump is associated with embedded clusters mainly toward the eastern edge of the clump only. These clusters show offsets of 20"-40" from the 12CO J=4-3 peak and are probably responsible for heating indicated by the derived high temperature. The N159W clump exhibits no sign of star formation toward the 12CO J=4-3 peak position and its western region. We suggest that the N159W peak represents a pre-star-cluster core of ~105M_sol which deserves further detailed studies. Note that recent star formation took place between N159W and N159E as indicated by several star clusters and HII regions, while the natal molecular gas toward the stars have already been dissipated by the ionization and stellar winds of the OB stars. The N159S clump shows little sign of star formation as is consistent with the lower temperature and somewhat lower density. The N159S clump is also a candidate for future star formation.

astro-ph.CO↗

arXiv2008

Centimeter Polarimetry of the R Coronae Australis Region

Circularly polarized 3.5 cm continuum emission was detected toward three radio sources in the R CrA region using the Very Large Array. The Class I protostar IRS 5b persistently showed polarized radio emission with a constant helicity over 8 yr, which suggests that its magnetosphere has a stable configuration. There is a good correlation between the Stokes I and Stokes V fluxes, and the fractional polarization is about 0.17. During active phases the fractional polarization is a weakly decreasing function of Stokes I flux, which suggests that IRS 5b is phenomenologically similar to other types of flare stars such as RS CVn binaries. The variability timescale of the polarized flux is about a month, and the magnetosphere of IRS 5b must be very large in size. The Class I protostar IRS 7A was detected once in circularly polarized radio emission, even though IRS 7A drives a thermal radio jet. This detection implies that the radio emission from the magnetosphere of a young protostar can escape the absorption by the partially ionized wind at least once in a while. The properties of IRS 7A and IRS 5b suggests that Class I protostars have organized peristellar magnetic fields of a few kilogauss and that the detectability of magnetospheric emission may depend on the evolutionary status of protostar. Also reported is the detection of circularly polarized radio emission toward the variable radio source B5.

astro-ph↗

arXiv2008

Resolving a Class I Protostar Binary System with Chandra

Using a sub-pixel event repositioning technique, we spatially resolved X-ray emission from the infrared double system IRS 5 in the R Corona Australis molecular cloud with ~0.8" separation. As far as we know, this result - obtained from 8 Chandra archival observations between 2000 and 2005 - is the first X-ray study of individual sources in a Class I protostar binary system with a projected separation of less than 200 AU. We extracted light curves and spectra of the individual sources using a two-dimensional image fitting method. IRS 5a at the south, the source which was brighter in the near-infrared, showed three X-ray flares lasting >20 ksec, reminiscent of X-ray flares from pre-main sequence stars, while the northern source (IRS 5b) was quiescent in X-rays in all the observations except for a 2005 August 9 observation with a factor of ~2 flux enhancement. In quiescence, these sources showed almost identical X-ray spectra, with NH ~4e22 cm-2, kT ~2 keV, and log Lx ~30.2-3 ergs s-1. IRS 5a showed plasma at temperatures up to kT ~5-6 keV during flares, while the column density of IRS 5b increased by a factor of 2 during an observation on 2005 August 9. We discuss the evolutionary stages and variation of the X-ray activity of these sources.

astro-ph↗

arXiv2008

Centimeter Imaging of the R Coronae Australis Region

The R CrA region was observed in the 3.5 and 6.2 cm continuum with high angular resolutions (0.6--1.7 arcseconds) using the Very Large Array. Archival data sets were also analyzed for comparison, which provided angular resolutions up to 0.3 arcseconds. A cluster of young stellar objects was detected, and a rich array of star forming activities was revealed. IRS 7A showed an enhanced outflow activity recently. The main peak of IRS 7A positionally coincides with an X-ray source, which suggests that the X-ray emission is directly related to the central protostar. The Class 0 source SMA 2 is associated with a double radio source, B 9a and 9b, and seems to be driving two outflows. The B 9 complex is probably a multiple-protostar system. Both B 9a and 9b are nonthermal radio sources with negative spectral indices. IRS 7B is a compact radio source surrounded by an extended structure. The compact source corresponds to the Class 0/I source SMA 1, and it is also closely associated with an X-ray source, suggesting that magnetic activities start early in the protostellar stage of evolution. The extended structure of IRS 7B may be a bipolar outflow. IRS 5 was resolved into two sources with a separation of 0.9 arcseconds. Both IRS 5a and 5b display radio flares and X-ray emission, suggesting that energetic magnetic processes are active in both members. The month-scale active phase of IRS 5b implies that the flare activity must involve large-scale magnetic fields. During the strong flare event of IRS 5b in 1998, IRS 5a also showed an enhanced level of radio emission. This concurrent activity suggests that IRS 5 may be an interacting young binary system, but the interaction mechanism is unknown. Alternatively, what was seen in the radio images could be a circumbinary halo.

astro-ph↗

arXiv2007

Ammonia Imaging of the Disks in the NGC 1333 IRAS 4A Protobinary System

The NGC 1333 IRAS 4A protobinary was observed in the ammonia (2, 2) and (3, 3) lines and in the 1.3 cm continuum with a high resolution (about 1.0 arcsec). The ammonia maps show two compact sources, one for each protostar, and they are probably protostellar accretion disks. The disk associated with IRAS 4A2 is seen nearly edge-on and shows an indication of rotation. The A2 disk is brighter in the ammonia lines but dimmer in the dust continuum than its sibling disk, with the ammonia-to-dust flux ratios different by about an order of magnitude. This difference suggests that the twin disks have surprisingly dissimilar characters, one gas-rich and the other dusty. The A2 disk may be unusually active or hot, as indicated by its association with water vapor masers. The existence of two very dissimilar disks in a binary system suggests that the formation process of multiple systems has a controlling agent lacking in the isolated star formation process and that stars belonging to a multiple system do not necessarily evolve in phase with each other.

astro-ph↗

arXiv2007

ASTE Submillimeter Observations of a Young Stellar Object Condensation in Cederblad 110

We present results of submillimeter observations of a low-mass young stellar objects (YSOs) condensation in the Cederblad 110 region of the Chamaeleon I dark cloud with Atacama Submillimeter Telescope Experiment. Our HCO+(J=4-3) map reveals a dense molecular gas with an extent of ~ 0.1 pc, which is a complex of two envelopes associated with class I sources Ced110 IRS4 and IRS11 and a very young object Cha-MMS1. The other two class I sources in this region, IRS6 and NIR89, are located outside the clump and have no extended HCO+ emission. HCO+ abundance is calculated to be 2.6 x 10^{-10} for MMS1 and 3.4 x 10^{-9} for IRS4, which are comparable to the reported value for other young sources. Bipolar outflows from IRS4 and IRS6 are detected in our 12CO(J=3-2) map. The outflow from IRS4 seems to collide with Cha-MMS1. The outflow has enough momentum to affect gas motion in MMS1, although no sign has been detected to indicate that a triggered star formation has occurred.

astro-ph↗

arXiv2005

Near Infrared Imaging Survey of Bok Globules: Density Structure

On the basis of near-infrared imaging observations, we derived visual extinction (Av) distribution toward ten Bok globules through measurements of both the color excess (E_{H-K}) and the stellar density at J, H, and Ks (star count). Radial column density profiles for each globule were analyzed with the Bonnor-Ebert sphere model. Using the data of our ten globules and four globules in the literature, we investigated the stability of globules on the basis of xi_max, which characterizes the Bonnor-Ebert sphere as well as the stability of the equilibrium state against the gravitational collapse. We found that more than half of starless globules are located near the critical state (xi_max = 6.5 +/- 2). Thus, we suggest that a nearly critical Bonnor-Ebert sphere characterizes the typical density structure of starless globules. Remaining starless globules show clearly unstable states (xi_max > 10). Since unstable equilibrium states are not long maintained, we expect that these globules are on the way to gravitational collapse or that they are stabilized by non-thermal support. It was also found that all the star-forming globules show unstable solutions of xi_max >10, which is consistent with the fact that they have started gravitational collapse. We investigated the evolution of a collapsing gas sphere whose initial condition is a nearly critical Bonnor-Ebert sphere. We found that the column density profiles of the collapsing sphere mimic those of the static Bonnor-Ebert spheres in unstable equilibrium. The collapsing gas sphere resembles marginally unstable Bonnor-Ebert spheres for a long time. We found that the frequency distribution of xi_max for the observed starless globules is consistent with that from model calculations of the collapsing sphere.

astro-ph↗