Kinematic Distance Research Articles

Radio observations of CTB80: detection of the snowplough in an old supernova remnant

New radio continuum and H i line observations of the old supernova remnant CTB80 are analysed. The radio continuum emission is more extended than previously known. We analyse archival ROSAT Position Sensitive Proportional Counter images of CTB80 and find extended X-ray emission associated with CTB80 over a 1°.2 diameter region. A new H i absorption spectrum towards the core of CTB80 yields a kinematic distance of ≃1.5 kpc. An analysis of the H i channel maps confirms the inner shell discovered by Koo et al. In addition, we discover an outer slowly moving shell centred on CTB80’s centre, with radius 76 arcmin and velocity 40 km s−1. The shell’s size and velocity are inconsistent with a stellar wind origin, but are consistent with what is expected for a cool dense shell in the cooling (snowplough) phase of a supernova remnant. Taking into account deceleration of the shell, its age also agrees with that of CTB80 (∼60 000 yr). The resulting picture of CTB80 is that of a large old supernova remnant, with an H i shell moving out slowly behind the slow outer shock and a hot interior which is still emitting X-rays and visible in the ROSAT images.

Star formation towards the Scutum tangent region and the effects of Galactic environment

By positional matching to the catalogue of Galactic Ring Survey molecular clouds, we have derived distances to 793 Bolocam Galactic Plane Survey (BGPS) sources out of a possible 806 located within the region defined by Galactic longitudes l = 28.5 degr to 31.5 degr and latitudes |b| < 1 degr. This section of the Galactic Plane contains several major features of Galactic structure at different distances, mainly mid-arm sections of the Perseus and Sagittarius spiral arms and the tangent of the Scutum-Centarus arm, which is coincident with the end of the Galactic Long Bar. By utilising the catalogued cloud distances plus new kinematic distance determinations, we are able to separate the dense BGPS clumps into these three main line-of-sight components to look for variations in star-formation properties that might be related to the different Galactic environments. We find no evidence of any difference in either the clump mass function or the average clump formation efficiency (CFE) between these components that might be attributed to environmental effects on scales comparable to Galactic-structure features. Despite having a very high star-formation rate, and containing at least one cloud with a very high CFE, the star formation associated with the Scutum-Centarus tangent does not appear to be in any way abnormal or different to that in the other two spiral-arm sections. Large variations in the CFE are found on the scale of individual clouds, however, which may be due to local triggering agents as opposed to the large-scale Galactic structure.

Distances of the TeV supernova remnant complex CTB 37 towards the Galactic bar

Three supernova remnants (SNRs) form the CTB 37 complex: CTB 37A (G348.5+0.1, associated with the TeV γ-ray source HESS J1714−385), CTB 37B (G348.7+0.3, associated with HESS J1713−381 and the magnetar CXOU J171405.7.381031) and G348.5−0.0. We use 21-cm H i absorption measurements to constrain kinematic distances to these SNRs, which have not previously been determined well. We revise the kinematic distance for CTB 37A to be in the range 6.3–9.5 kpc (previously ∼11.3 kpc) because it is beyond the near 3-kpc arm and in front of the far side of the CO cloud at −145 km s−1 towards l= 348.5. G348.5−0.0 has an H i column density (⁠∼6.1×1021 cm−2) lower than CTB 37A (∼7.1 × 1021 cm−2). Also, G348.5−0.0 does not have the major absorption feature at −107 km s−1 that CTB 37A shows. This is caused by the near 3-kpc arm, so G348.5−0.0 is at a distance of ≤6.3 kpc. CTB 37B is at a distance of ∼13.2 kpc (previously 5–9 kpc) based on: (1) it has an absorption feature at −10 ± 5 km s−1 from the far 3-kpc arm, so CTB 37B is behind it; (2) there is absorption at −30 km s−1 but not at −26 km s−1, which yields the distance value; and (3) the H i column density towards CTB 37B (∼8.3 × 1021 cm−2) is larger than that towards CTB 37A. In summary, CTB 37A, CTB 37B and G348.5+0.0 are all at different distances and are only by chance nearby each other on the sky. In addition, we conclude that CTB 37A and 37B are not associated with the historical supernova AD 393.

PLANETARY CONSTRUCTION ZONES IN OCCULTATION: DISCOVERY OF AN EXTRASOLAR RING SYSTEM TRANSITING A YOUNG SUN-LIKE STAR AND FUTURE PROSPECTS FOR DETECTING ECLIPSES BY CIRCUMSECONDARY AND CIRCUMPLANETARY DISKS

<abridged> The large relative sizes of circumstellar and circumplanetary disks imply that they might be seen in eclipse in stellar light curves. We estimate that a survey of ~10^4 young (~10 Myr old) post-accretion pre-MS stars monitored for ~10 years should yield at least a few deep eclipses from circumplanetary disks and disks surrounding low mass companion stars. We present photometric and spectroscopic data for a pre-MS K5 star (1SWASP J140747.93-394542.6), a newly discovered ~0.9 Msun member of the ~16 Myr-old Upper Cen-Lup subgroup of Sco-Cen at a kinematic distance of 128 pc. SuperWASP and ASAS light curves for this star show a remarkably long, deep, and complex eclipse event centered on 29 April 2007. At least 5 multi-day dimming events of >0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of ~1 mag eclipses symmetrically occurring +-12 days and +-26 days before and after. Hence, significant dimming of the star was taking place on and off over at least a ~54 day period in 2007, and a strong >1 mag dimming event occurred over a ~12 day span. We place a firm lower limit on the period of 850 days (i.e. the orbital radius of the eclipser must be >1.7 AU and orbital velocity must be <22 km/s). The shape of the light curve is similar to the lop-sided eclipses of the Be star EE Cep. We suspect that this new star is being eclipsed by a low-mass object orbited by a dense inner disk, girded by at least 3 dusty rings of lower optical depth. Between these rings are at least two annuli of near-zero optical depth (i.e. gaps), possibly cleared out by planets or moons, depending on the nature of the secondary. For possible periods in the range 2.33-200 yr, the estimated total ring mass is ~8-0.4 Mmoon (if the rings have optical opacity similar to Saturn's rings), and the edge of the outermost detected ring has orbital radius ~0.4-0.09 AU.

Mass distribution of the Galaxy with VERA

AbstractWe aim to reveal the mass distribution of the Galaxy based on a precise rotation curve constructed using VERA observations. We have been observing Galactic H2O masers with VERA. We here report one of the results of VERA for IRAS 05168+3634. The parallax is 0.532 ± 0.053 mas which corresponds to a distance of 1.88+0.21−0.17 kpc, and the proper motions are (μαcosδ, μδ) = (0.23 ± 1.07, −3.14 ± 0.28) mas yr−1. The distance is significantly smaller than the previous distance estimate of 6 kpc based on a kinematic distance. This drastic change places the source in the Perseus arm rather than in the Outer arm. Combination of the distance and the proper motions with the systemic velocity provides a rotation velocity of 227+9−11 km s−1 at the source assuming Θ0 = 240 km s−1. The result is marginally slower than the rotation velocity at LSR with ~ 1−σ significance, but consistent with previous VLBI results for six sources in the Perseus arm. We also show the averaged disk peculiar motion over the seven sources in the Perseus arm as (Umean, Vmean) = (11 ± 3, −17 ± 3) km s−1. It suggests that the seven sources in the Perseus arm are systematically moving toward the Galactic center, and lag behind the Galactic rotation with more than 3-σ significance.

Annual Parallax Measurements of an Infrared Dark Cloud MSXDC G034.43+00.24

AbstractWe have measured the annual parallax of the H2O maser associated with an infrared dark cloud, MSXDC G034.43+00.24, with VERA. The parallax is 0.643 ± 0.049 mas, corresponding to a distance of 1.56+0.12−0.11 kpc. This value is less than half of the previous kinematic distance of 3.7 kpc. We revised the core-mass estimates of MSXDC G034.43+00.24 from the previous estimations of 1000M⊙ to hundreds of M⊙. The spectral type is still consistent with that of the massive star.

New white dwarfs in the Hyades

On the basis of the PPMXL catalogue (R\"oser, Demleitner & Schilbach, 2010) we searched for white dwarfs that are also member candidates of the Hyades in a region up to 40 pc from the cluster centre. We use the proper motions from PPMXL in the convergent point method to determine probable kinematic members. We cross-match the kinematic candidates with catalogues containing white dwarfs and, finally, check the kinematic with the photometric distances for consistency. We find the 10 classical white dwarfs in the Hyades and determine their individual kinematic distances. Additionally, we identified 17 new probable (former) Hyades white dwarfs, i.e. white dwarfs co-moving with the bulk space motion of the Hyades cluster. At present, none of them can be excluded from membership on the basis of the measured radial velocities. For another 10 objects, the kinematic and the photometric distances are discordant which rates them as probable non-members. Among the probable members, five white dwarfs are in binary systems, three are known, two are new. There is good indication for an empirical magnitude-distance (from centre) relation, such that the dimmer white dwarfs are farther away from the cluster centre than the brighter ones. Our sample is getting incomplete close behind the centre of the cluster. Follow-up observations are encouraged to independently confirm the predicted radial velocities and the distances of the candidates.

Searching for the Perseus arm in the anticenter direction

Here we propose a two step approach to provide new insights on the outer spiral arm pattern of the Milky Way: 1) a Stromgren photometric survey to map the stellar space density of moderate young type stars tracing the Perseus arm, and 2) a spectroscopic survey to determine the velocity perturbation due to the density wave through accurate Radial Velocity (RV, hereafter). First reduced preliminary data suggest an overdensity around 1.5–2 kpc, probably associated with the Perseus arm. Results from this project will present a significant step towards mapping the spiral structure between the second and the third galactic quadrant, where the determination of kinematic distances is not possible.

H2O Maser Motions and the Distance of the Star-Forming Region G 192.16−3.84

Abstract We present the results of astrometic observations of H$_{2}$O masers associated with the star-forming region G 192.16$-$3.84 with the VLBI Exploration of Radio Astrometry (VERA). The H$_{2}$O masers seem to be associated with two young stellar objects (YSOs) separated by $\sim\ $1200 AU, as reported in previous observations. In the present observations, we successfully detected an annual parallax of $\pi$$=$ 0.66$\ \pm\ $0.04 mas for the H$_{2}$O masers, which corresponds to a distance to G 192.16$-$3.84 of $D$$=$ 1.52$\ \pm\ $0.08 kpc from the Sun. The determined distance is shorter than the estimated kinematic distance. Using the annual parallax and the estimated parameters of the millimeter continuum emission, we estimate the mass of the disk plus circumstellar cloud in the southern YSO to be 10.0$^{+4.3}_{-3.6}\ M_{\odot}$. We also estimate the galactocentric distance and the peculiar motion of G 192.16$-$3.84, relative to a circular galactic rotation, to be $R_{\ast}$$=$ 9.99$\ \pm\ $0.08 kpc and $Z_{\ast}$$=$$-$0.10$\ \pm\ $0.01 kpc, and ($U_{\ast}$, $V_{\ast}$, $W_{\ast}$) $=$ ($-$2.8$\ \pm\ $1.0, $-$10.5$\ \pm\ $0.3, 4.9$\ \pm\ $2.7) [km s$^{-1}$], respectively. The peculiar motion of G 192.16$-$3.84 is not beyond the range of recent VLBI astrometric results. The angular distribution and three-dimensional velocity field of H$_{2}$O maser features indicate the existence of a bipolar outflow with a major axis along the northeast–southwest direction.

The RMS survey: resolving kinematic distance ambiguities towards a sample of compact H ii regions using H i absorption★

We present high-resolution HI data obtained using the Australia Telescope Compact Array to resolve the near/far distance ambiguities towards a sample of compact HII regions from the Red MSX Source (RMS) survey. The high resolution data are complemented with lower resolution archival HI data extracted from the Southern and VLA Galactic Plane surveys. We resolve the distance ambiguity for nearly all of the 105 sources where the continuum was strong enough to allow analysis of the HI absorption line structure. This represents another step in the determination of distances to the total RMS sample, which with over 1,000 massive young stellar objects and compact HII regions, is the largest and most complete sample of its kind. The full sample will allow the distribution of massive star formation in the Galaxy to be examined.

A SURVEY OF RADIO RECOMBINATION LINES USING THE OOTY RADIO TELESCOPE AT 328 MHz IN THE INNER GALAXY

A survey of radio recombination lines in the Galactic plane with longitude $-32^o < l < +80^o$ and latitude $b<\pm3^o$ using Ooty Radio Telescope(ORT) at 328 MHz has been reported. ORT observations were made using a New Digital Backend(NDB) augmented to it recently. With NDB ORT had a beam of $2^o.3 \times 2^o.2 sec(\delta)$ and a passband of $\sim$1 MHz in the spectral line mode. The above mentioned Galactic region was divided into $\sim 2^o \times 2^o$ patches with the ORT beam pointed to the center. The ORT observations form a study of distribution of extended low-density warm-ionized medium(ELDWIM) in the inner Galaxy using H271$\alpha$ RL. By obtaining kinematical distances using $V_{LSR}$ of the H271$\alpha$ RLs the distribution of ELDWIM clouds within the inner Galaxy has been deduced for the region given above.

The G305 star-forming complex: the central star clusters Danks 1 and Danks 2

The G305 HII complex (G305.4+0.1) is one of the most massive star forming structures yet identified within the Galaxy. It is host to many massive stars at all stages of formation and evolution, from embedded molecular cores to post main-sequence stars. Here, we present a detailed near-infrared analysis of the two central star clusters Danks 1 and Danks 2, using HST+NICMOS imaging and VLT+ISAAC spectroscopy. We find that the spectro-photometric distance to the clusters is consistent with the kinematic distance to the G305 complex, an average of all measurements giving a distance of 3.8\pm0.6kpc. From analysis of the stellar populations and the pre-main-sequence stars we find that Danks 2 is the elder of the two clusters, with an age of 3^{+3}_{-1}Myr. Danks 1 is clearly younger with an age of 1.5^{+1.5}_{-0.5}Myr, and is dominated by three very luminous H-rich Wolf-Rayet stars which may have masses \geq100\msun. The two clusters have mass functions consistent with the Salpeter slope, and total cluster masses of 8000\pm1500\msun\ and 3000\pm800\msun\ for Danks 1 and Danks 2 respectively. Danks 1 is significantly the more compact cluster of the two, and is one of the densest clusters in the Galaxy with $\log (\rho/M_{\odot}{\rm pc}^{-3}) = 5.5^{+0.5}_{-0.4}$. In addition to the clusters, there is a population of apparently isolated Wolf-Rayet stars within the molecular cloud's cavity. Our results suggest that the star-forming history of G305 began with the formation of Danks 2, and subsequently Danks 1, with the origin of the diffuse evolved population currently uncertain. Together, the massive stars at the centre of the G305 region appear to be clearing away what is left of the natal cloud, triggering a further generation of star formation at the cloud's periphery.

Mass reservoirs surrounding massive infrared dark clouds

Context: Infrared Dark Clouds (IRDCs) harbor progenitors of high-mass stars. Little is known of the parental molecular clouds of the IRDCs. Aims: We demonstrate the feasibility of the near-infrared (NIR) dust extinction mapping in tracing the parental molecular clouds of IRDCs at the distances of D = 2.5 - 8 kpc. Methods: We derive NIR extinction maps for 10 prominent IRDC complexes using a color-excess mapping technique and NIR data from the UKIDSS/Galactic Plane Survey. We compare the resulting maps to the 13CO emission line data, to the 8 \mu m dust opacity data, and to the millimeter dust emission data. We derive distances for the clouds by comparing the observed NIR source densities to the Besancon stellar distribution model and compare them to the kinematic distance estimates. Results: The NIR extinction maps provide a view to the IRDC complexes over the dynamical range of Av = 2 - 40 mag, in spatial resolution of 30". The NIR extinction data correlate well with the 13CO data and probe a similar gas component, but also extend to higher column densities. The NIR data reveal a wealth of extended structures surrounding the dense gas traced by the 8 \mu m shadowing features and sub-mm dust emission, showing that the clouds contain typically > 10 times more mass than traced by those tracers. The IRDC complexes of our sample contain relatively high amount of high-column density material, and their cumulative column density distributions resemble active nearby star-forming clouds like Orion rather than less active clouds like California. Conclusions: NIR dust extinction data provide a new powerful tool to probe the mass distribution of the parental molecular clouds of IRDCs up to the distances of D = 8 kpc. This encourages for deeper NIR observations of IRDCs, because the sensitivity and resolution of the data can be directly enhanced with dedicated observations.

MOLECULAR ENVIRONMENT AND AN X-RAY SPECTROSCOPY OF SUPERNOVA REMNANT KESTEVEN 78

We investigate the molecular environment of the Galactic supernova remnant (SNR) Kesteven 78 and perform an XMM-Newton X-ray spectroscopic study for the northeastern edge of the remnant. SNR Kes78 is found to interact with the molecular clouds (MCs) at a systemic local standard of rest velocity of 81km/s. At around this velocity, the SNR appears to contact a long molecular strip in the northeast and a large cloud in the east as revealed in the 13CO line, which may be responsible for the radio brightness peak and the OH maser, respectively. The 12CO-line bright region morphologically matches the eastern bright radio shell in general, and the SNR is consistent in extent with a CO cavity. Broadened 12CO line profiles discerned in the eastern maser region and the western clumpy molecular arc and the elevated 12CO J=2-1/J=1-0 ratios along the SNR boundary may be signatures of shock perturbation in the molecular gas. The SNR-MC association places the SNR at a kinematic distance of 4.8 kpc. The X-rays arising from the northeastern radio shell are emitted by underionized hot (~1.5 keV), low-density (~0.1 cm^{-3}) plasma with solar abundance, and the plasma may be of intercloud origin. The age of the remnant is inferred to be about 6 kyr. The size of the molecular cavity in Kes78 implies an initial mass around 22Msun for the progenitor.

THE BOLOCAM GALACTIC PLANE SURVEY. VII. CHARACTERIZING THE PROPERTIES OF MASSIVE STAR-FORMING REGIONS

We present the results of a GBT survey of NH3(1,1), (2,2), (3,3) lines towards 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic longitudes in the inner Galaxy. We have detected the NH3(1,1) line towards 72% of our targets (456), demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas. We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH3. The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms, with the number of sources peaking between Galactocentric radii of 4-5 kpc. We measure the physical properties of each source and find that depending on the distance, BGPS sources are primarily clumps, with some cores and clouds. We have examined the physical properties as a function of Galactocentric distance, and find a mean gas kinetic temperature of 15.6 K, and that the NH3 column density and abundance decrease by nearly an order of magnitude between Galactocentric radii of 3 - 11 kpc. Comparing sources at similar distances demonstrates that the physical properties are indistinguishable, which suggests a similarity in clump structure across the Galactic disk. We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al. and Lada et al., and massive star formation presented by Kauffmann et al. 48% of our sample should be forming stars (including massive stars) with high efficiency, and 87% contain subregions that should be efficiently forming stars. Indeed, we find that 67% of the sample exhibit signs of star formation activity based on an association with a mid-IR source.

Distances to southern 6.7-GHz methanol masers through H i self-absorption

We present the kinematic distance ambiguity resolutions of over 400 6.7-GHz methanol masers. Using the data sets of the International Galactic Plane Survey we have extracted H i spectra towards the sites of methanol maser emission between longitudes 270° and 67° and examined them for evidence of H i self-absorption. Using well-established criteria we identify 442 resolutions (classified by reliability) with a 1.07:1.11 ratio between near and far kinematic distance assignments. For a sub-sample of 118, we compare our resolutions with those of the literature and find 85 ± 10 per cent agreement. Using the distances we examine the Galactocentric distribution and properties of the masers. We also compare 6.7-GHz maser velocities with those of CS, finding the maser mid-velocity is closely correlated with the CS velocity, typically to within 2.8 km s−1.

Accuracy Diagrams for the Galactic Rotation Curve and Kinematical Distances

We revisit methods used to determine the Galactic rotation curve and kinematical distances from radial velocities and proper motions. We construct ``accuracy diagrams'' to show the distributions in the galactic plane of expected uncertainties in the derived quantities, such as rotation velocities and kinematical distances. We discuss how to optimize the source selection for measurements of kinematical quantities based on accuracy diagrams.

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

Abstract We performed the astrometry of H$_2$O masers in the Galactic star-forming region G48.61$+$0.02 with the VLBI Exploration of Radio Astrometry (VERA). We derived a trigonometric parallax of 199$\ \pm\ $7$\ \mu$as, which corresponds to a distance of 5.03$\ \pm\ $0.19 kpc. The distance to G48.61$+$0.02 is about half of its far kinematic distance, which was often assumed previously. This distance places G48.61$+$0.02 in the Sagittarius–Carina arm, and near to the active star-forming region and the supernova remnant W 51. We also obtained the three-dimensional motion of G48.61$+$0.02, and found that it has a large peculiar motion of 40$\ \pm\ $5 km s$^{-1}$. This peculiar motion would have originated along with multiple supernovae explosions in W 51, or streaming motion across the Sagittarius–Carina arm.

A H2CO and H110αsurvey of H ii regions with the 25-m radio telescope of Nanshan Station

Context. Accurate distances are necessary for determining the physical properties of massive star-formation regions and the structure of our Galaxy. One way to approach these studies is by determining the kinematic distances of H II regions.

THE STELLAR CONTENT OF OBSCURED GALACTIC GIANT H II REGIONS. VII. W3

Spectrophotometric distances in the K band have been reported by different authors for a number of obscured Galactic HII regions. Almost 50% of them show large discrepancies compared to the classical method using radial velocities measured in the radio spectral region. In order to provide a crucial test of both methods, we selected a target which does not present particular difficulty for any method and which has been measured by as many techniques as possible. The W3 star forming complex, located in the Perseus arm, offers a splendid opportunity for such a task. We used the NIFS spectrograph on the Frederick C. Gillett Gemini North telescope to classify candidate "naked photosphere" OB stars based on 2MASS photometry. Two of the targets are revealed to be mid O-type main sequence stars leading to a distance of d = 2.20 kpc. This is in excellent agreement with the spectrophotometric distance derived in the optical band (d = 2.18 kpc, Humphreys 1978) and with a measurement of the W3 trigonometric parallax (d = 1.95 kpc, Xu et al. 2006). Such results confirm that the spectrophotometric distances in the K band are reliable. The radio derived kinematic distance, on the contrary, gives a distance twice as large (d = 4.2 kpc, Russeil 2003). This indicates that this region of Perseus arm does not follow the Galactic rotation curve, and this may be the case also for other HII regions for which discrepancies have been found.