LSR Velocity Research Articles

VLBI Imaging of the 86 GHz SiO Maser Emission in the Circumstellar Envelope of VX Sagittarii

We have observed and imaged the SiO maser source in the late-type star VX Sgr with a single VLBI baseline at 3.5 mm wavelength. Phase-referenced channel maps with a beamwidth of ~0.4 mas show multiple components over a LSR velocity range of -1 to 24 km s-1, and many of the maser features display velocity widths smaller than 1 km s-1. The maser spots in this 86 GHz transition (v = 1, J = 2 → 1) are arranged in an irregular ring-shaped configuration of diameter ~30 mas, echoing the structures found in the J = 1 → 0 transition at 43 GHz around several Mira variables and VX Sgr itself. Unlike previous observations of SiO masers, in VX Sgr we detect a clear, systematic velocity gradient of ~0.6 km s-1 AU-1 among the strongest complex of masers on the southernmost portion of the ring structure. This velocity gradient can be interpreted as a rigid rotation of the circumstellar envelope with v sin i ~ 13 km s-1. Maser emission is not detected on long (5000 km) baselines, which places a 0.1 mas lower limit on the size of strong maser spots.

4.9. Molecular abundances in G1.6-0.025

G1.6-0.025 is a dense molecular cloud, located near the Galactic Centre at l=1.6° and b=−0.025°. Lacking in star-forming or infra-red regions, the cloud was first detected as a prominent 5-GHz H2CO absorption feature (Whiteoak & Gardner 1979). NH3 observations by Gardner et al (1985) revealed a clumpy cloud with a diameter of about 30 parsec, average LSR velocity of 50 km s−1, and a kinetic temperature exceeding 50 K. In addition, a high-velocity component at 160 km s−1 has been detected towards one of the clumps (Gardner & Boes 1987). CH3OH in the cloud gives rise to a 12-GHz 20−3_1 E transition in absorption, representing the best example of rare population ‘anti-inversion’ for this transition (Whiteoak & Peng 1989; Peng & Whiteoak 1993). In contrast, the 36-GHz 4−1−30 E transition shows extended emission with superimposed knots containing maser emission (Haschick & Baan, 1993). Sobolev (1996) has suggested that a collision! has occurred between the main cloud and another cloudlet with relative velocity of 100 km s−1, resulting in high kinetic temperatures and shock waves that create the CH3OH masers.

Ultraviolet Interstellar Absorption Lines toward the Starburst Dwarf Galaxy NGC 1705

Archival Goddard High Resolution Spectrograph (GHRS) low-resolution spectra of NGC 1705, with wavelength ranges of 1170.3-1461.7 A and 1453.5-1740.1 A and a velocity resolution of ~120 kms-1, have been used to derive the velocity structure and equivalent widths of the absorption lines of Si II λ1190.42, λ1260.42, λ1304.37, and λ1526.71, S II λ1253, Al II λ1670.79, and Fe II λ1608.45 in this sight line. Three relatively narrow absorption components are seen at LSR velocities of -20 kms-1, 260 kms-1, and 540 kms-1. Arguments are presented to show that these absorption features are interstellar rather than stellar in origin on the basis of a comparison with the C III λ1175.7 absorption feature. We identify the -20 kms-1 component with Milky Way disk and halo gas and the 260 kms-1 component with an isolated high-velocity cloud, HVC 487. This small HVC is located ~10° from the H I gas that envelops the Magellanic Clouds and the Magellanic Stream (MS). The Si/H ratio for this HVC is greater than 0.6(Si/H)☉, which with velocity agreement suggests association with the Magellanic Cloud and MS gas. Hα emission line kinematics of NGC 1705 show the presence of a kiloparsec-scale expanding supershell of ionized gas centered on the central nucleus with a blueshifted emission component at 540 kms-1. We identify the 540 kms-1 absorption component seen in the GHRS spectra with the front side of this expanding, ionized supershell. The most striking feature of this component is strong Si II and Al II absorption but weak Fe II λ1608 absorption. The low Fe II column density derived is most likely intrinsic since it cannot be accounted for by ionization corrections or dust depletion. Because of their shallow gravitational potential wells, dwarf galaxies have small gravitational binding energies and are vulnerable to large mass losses from strong winds driven by the supernovae from the first generation of stars. Galactic winds from dwarf galaxies occur at timescales less than 108 yr, which is less than the timescale required to produce Type Ia supernovae. Consistent with our observations, shells produced by galactic winds are expected to be enriched with Type II supernova products like Si, Al, and Mg and should be deficient in the products of Type Ia supernovae, like Fe and iron-peak elements.

The HiiRegion Sharpless 269. I. Morphological Study of the Radial Velocity, Velocity Dispersion, and Density Fields

We present [S II] λλ6716.5, 6730.8 radial velocity, velocity dispersion, and density field maps of the H II region Sharpless 269 obtained using a scanning Fabry-Perot interferometer. The radial velocity field shows a clear bipolar morphology probably related to the dust/molecular lane bisecting the H II region. The mean LSR velocity (VLSR) extracted from the data is 16.45 ± 0.03 km s-1 (1 σ = 2.77 ± 0.02 km s-1), blueshifted by 1.3 km s-1 from the associated molecular cloud. The mean velocity dispersion given by subtraction of the instrumental and thermal Doppler broadenings from the FWHM of the line profiles is 16.43 ± 0.10 km s-1 (1 σ = 10.40 ± 0.07 km s-1). Line width analysis yields an east-west gradient caused by the proximity of molecular material and the outflow from a young stellar object in the western part of the nebula. The electron density field has a mainly uniform distribution but for a localized increase positionally associated with the young stellar object mentioned above. The mean density is found to be 290 ± 2 cm-3, while the maximum of the density distribution is centered near 200 cm-3. Overall, the results are in good agreement with an expansion scenario for the ionized gas except for the density field which fails to exhibit the predicted exponential drop from the exciting star to the edge of the H II region.

VLA H92α and H115β Recombination Line Observations of the Galactic Center HiiRegions: The Sickle (G0.18−0.04) and the Pistol (G0.15−0.05)

The Very Large Array has been used in the CnB and DnC configurations to observe the remarkable Galactic center sources, the Sickle and the Pistol, near l = 018, b = -004. These H II regions have an unusual morphology and may be physically associated with the linear nonthermal filaments at l = 018, which appear to intersect the sources. The H92α (8.31 GHz) and H115β (8.43 GHz) radio recombination lines arising from these sources have been observed with angular resolutions of 6'' and 9'', respectively. In addition, there is a probable detection of the helium line in the Pistol (Y+ ~ 14% ± 6%), while in the Sickle, no helium lines were detected with an upper limit of Y+ ~ 5% (3 σ). A complex velocity field has been observed in both sources. The LSR velocity in the Sickle varies from 0 to 75 km s-1, with an average velocity of ~35 km s-1; the average velocity of the Pistol is ~115 km s-1. The recombination line properties of the Sickle and the Pistol (FWHM line widths, line-to-continuum ratios, β-to-α ratio) are consistent with photoionization from hot stars. The β-to-α line ratio of ~0.35 ± 0.07 over most of the Sickle and Pistol does not differ significantly from the LTE value of 0.28. The average LTE electron temperature, T*e, for the Sickle (~5500 K) is similar to typical Galactic center H II regions, and T*e for the Pistol is somewhat lower (~3600 K). An additional H II component in the line profiles of three regions of the Sickle in which the nonthermal filaments are present suggests that an interaction between the ionized gas and the nonthermal filaments is occurring. The probable detection of He92α in the Pistol and the nondetection in the Sickle may be due to a difference in the radiation field of the ionizing sources.

Kinematical Structure of the Local Interstellar Medium

AbstractObservations of interstellar Na I in the spectra of 93 stars within 315 pc from the Sun show that it lies in a tunnel of gas moving away from Scorpio-Centaurus and is surrounded by gas moving toward the Galactic center.Gas approaches the Sun from Scorpio-Centaurus expanding from (r, l, b)=(160 pc, 313°7, +28°2) with LSR velocity 15.3 km s−1. The radius of this shell is 153 pc.We identify these clouds:D: velocity vector (υd, ld, bd)=(+7.2 km s−1, 305°1, −13°5), above and below the Galactic plane (GP) in the range of Galactic longitudes 357°–55°.C: velocity vector (υc, lc, bc)=(+11.5 km s−1, 349°0, −35°2), above and below the GP in the range 30°≤l≤110°.M: velocity vector (υm, lm, bm)=(+21.9 km s−1, 34°2, +1°5), above and below the GP in the range 100°≤l≤130°.P: velocity vector (υp, lp, bp)=(+13.8 km s−1, 244°9, +5°4), above and below the GP from l~120° to the limit of our data at l~210°.E: velocity vector (υe, le, be)=(+16.8 km s−1, 208°4, +6°2) in the range 160°≤l≤185° and −10°≤b≤–35°.A: velocity vector (υa, la, ba)=(+12.9 km s−1, 73°6, −5°6) towards the Galactic anti-center, below the GP.I: velocity vector (υi, li, bi)=(+37.7 km s−1, 132°8, −64°3) towards the Galactic anti-center, above the GP.

A Catalog of Molecular Gas at High Galactic Latitudes

view Abstract Citations (82) References (108) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Catalog of Molecular Gas at High Galactic Latitudes Magnani, Loris ; Hartmann, Dap ; Speck, Bryan G. Abstract The global distribution and physical properties of the high-latitude molecular clouds are tabulated and discussed. As of this writing, more than 100 objects have been identified at Galactic latitudes |b| > 25°. Positions are listed for all the known clouds and LSR velocity, angular extent, mass, and internal velocity dispersion are listed when such data are available from the literature. The high-latitude molecular clouds consist primarily of translucent clouds, so that this catalog is the largest, most complete compendium of these objects at high Galactic latitudes. The velocity dispersion of the ensemble of clouds is 5.8 km s-1 if seven intermediate velocity objects are excluded and 9.9 km s-1 otherwise. The former dispersion implies a scale height for the clouds of 124 pc and a mean distance of 150 pc; the latter dispersion yields 210 pc and 260 pc, respectively. Thus, the majority of high-latitude clouds are local objects that may be situated at the nearer edges of the Local Bubble. As a group, they are the nearest molecular clouds to the Sun. The average velocity of the ensemble of clouds is -0.3 km s-1 without the intermediate velocity objects and -2.4 km s-1 including these clouds. From the catalog of clouds, we determine values for the filling fraction and mass surface density of the high-latitude molecular clouds (and thus of translucent gas) of 0.005 and 0.1-0.2 M0 pc -2, respectively, at |b| > 25°. Including the lower latitude contribution, we estimate the total local mass surface density of translucent clouds to be 0.2-0.3 Msun pc-2 In the local interstellar medium, these objects represent from 10% to 20% of the molecular gas inventory. Individual clouds range in size from less than 10-1 to 101 pc and in mass from 10-1 to 103 Msun. An asymmetry between the northern and southern Galactic hemisphere distribution of the clouds can be interpreted as a displacement of the Sun from the Galactic midplane of 18 pc, a value consistent with determinations based on other tracers. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1996 DOI: 10.1086/192344 Bibcode: 1996ApJS..106..447M Keywords: CATALOGS; GALAXY: STRUCTURE; ISM: CLOUDS; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES full text sources ADS | data products SIMBAD (121)

Three Millimeter Molecular Line Observations of Sagittarius B2. II. High-Resolution Studies of C 18O, HNCO, NH 2CHO, and HCOOCH 3

High-resolution imaging of C<SUP>18</SUP>O, HNCO, NR<SUB>2</SUB>CHO, and RCOOCH<SUB>3</SUB> in Sgr B2 are presented in this study. The C<SUP>18</SUP>O emission comes mainly from the Sgr B2(M) and Sgr B2(N) dense cores and the western gas clump RNO(M). Toward Sgr B2(M), the C<SUP>18</SUP>O column density is 2 times higher and the fractional abundance is 80 times higher than toward Sgr B2(N). In HNO(M), the narrow line width implies that the C<SUP>18</SUP>O emission arises from the diffuse gas. The complex molecules NR<SUB>2</SUB>CHO and HCOOCR<SUB>3</SUB> were detected only toward the Sgr B2(N) core. The HNCO K<SUB>-1</SUB> = 2 emission is detected only in Sgr B2(N) and is attributed to efficient radiative pumping, which indicates the significant presence of far-infrared field and warm dust grains. Only 4% of the HNCO was found in the K<SUB>-1</SUB> = 0 ladders in Sgr B2(N). The nondetection of the K<SUB>-1</SUB> = 2 emission toward Sgr B2(M) is caused by excitation and low abundance. In contrast, the HNCO K<SUB>-1</SUB> = 0 emission comes mainly from the extended gas component: the far northern region and HNCO(SW). For the K<SUB>-1</SUB> = 0 transitions, T<SUB>rot</SUB> = ∼7 K. The low T<SUB>rot</SUB> and the apparent ubiquity of RNCO suggest that abundant HNCO exists in the Sgr B2 envelope. The HNCO K<SUB>-1</SUB> = 0 emission unveiled two spatially extended velocity components; the velocity gap between them covers the same LSR velocities of the Sgr B2 dense cores. If HNCO is formed via surface reactions, the pervasive detection of HNCO in the outer edges of Sgr B2 cloud core leads to the cloud-cloud collision postulate. <P />A north-south C<SUP>18</SUP>O bipolar structure was seen in Sgr B2(M) centered at the compact H II region F. The bipolar structure appears asymmetric and thus favors the outflow interpretation. The sharp outer edges of the C<SUP>18</SUP>O line profiles of the two lobes further support the outflow picture. The estimated outflow age is ∼2±1 x 10<SUP>4</SUP> yr, and the total mass is ∼1700 M<SUB>sun</SUB>. The outflow masses for the blue and red lobes are &lt;360 M<SUB>sun</SUB> and &lt;410 M<SUB>sun</SUB>, respectively. The mass-loss rate is thus &lt;0.037 M<SUB>sun</SUB> yr<SUP>-1</SUP>. The detection of outflows in Sgr B2(M) supports the gas dispersal picture and subsequent chemical variations disclosed by the HNO and HC<SUP>13</SUP>CCN emission void. Three distinct velocity components toward Sgr B2(N) were seen from the HNCO K<SUB>-1</SUB> = 2 emission. The broad component is centered at the H II region K2 with a north-south velocity gradient, which is probably due to rotation. The mass of the rotating cloud is between ∼630 and 1570 M<SUB>sun</SUB>. The two narrow components are located on the opposite sides of the K1-K2 ridge and are in fact the two lobes of a gas outflow. The estimated outflow age of Sgr B2(N) is ∼6 x 10<SUP>3</SUP> yr, which is a factor of 3 younger than Sgr B2(M). The outflow masses are ≤200 and ≤300 M<SUB>sun</SUB> for the red and blue lobes, respectively. This yields a mass-loss rate &lt;0.08 M<SUB>sun</SUB> yr<SUP>-1</SUP>, about 2 times higher than that of Sgr B2(M). All these suggest that Sgr B2(N) is much younger than Sgr B2(M). Finally, high-resolution imaging of the radiatively excited HNCO K<SUB>-1</SUB> = 2 transition allows the separation of an apparent bipolar structure into a gas outflow and a rotating disk cloud.

A High-Resolution Survey of Interstellar CA II Absorption

We present high-resolution (0.3-1.2 km s<SUP>-1</SUP>) spectra, obtained with the AAT UHRF and/or the KPNO coudé feed, of interstellar Ca II absorption toward 44 Galactic stars. For most stars in the sample, these new spectra are characterized by higher resolution, higher S/N, and/or wider velocity coverage than previously available spectra. As was found in a similar high-resolution survey of Na I absorption, the Ca II profiles show complex structure in many lines of sight. Multicomponent fits to the line profiles yield estimates for the column densities, line widths, and velocities for 417 individual interstellar cloud components; an analysis of the component separations suggests that we may have discerned only about 40% of the components actually present, however. The mean LSR velocities of the Ca II and Na I absorption are similar, but the Ca II velocity distribution is broader, due to outlying components seen only in Ca II. The Ca II line widths imply that at most 40% of the Ca II components in the present sample could arise in warm gas at T ≥ 6000 K. If most gas traced by Ca II is warmer than 500 K, then the turbulent velocities in that gas must generally be subsonic. In general, the Ca II component line widths are larger than those of corresponding Na 1 components seen at the same velocity, suggesting that the Ca II occupies a somewhat larger volume, characterized by a larger temperature and/or turbulent velocity, than that occupied by the Na I. Ca II absorption can arise both in cold, relatively dense gas, where Ca is typically heavily depleted onto grains and Ca II can be its dominant ionization state, and also in warmer, lower density gas, where Ca is less depleted but Ca II is a trace ionization state. The interplay between the strong effects of Ca ionization balance and Ca depletion, for different types of neutral gas, can explain the similarities between the line profiles seen for Ca II and for various dominant first ions of less depleted elements. High-resolution spectra of Ca II can thus be useful for interpreting lower resolution UV spectra of many other species found in neutral clouds. The ratio of the column densities of Na I and Ca II is not an unambiguous indicator of Ca depletion and cloud physical conditions, and it can vary by factors of more than 30 for adjacent components separated by only several km s<SUP>-1</SUP>; "individual" components derived from lower resolution spectra thus may often be blends of several distinct and physically different parcels of gas.

A study of the time variation of LSR velocity of recently discovered H 2O 6 16−5 23 masers

We study the time variation in the LSR velocities of our recently discovered H 2O 6 16−5 23 masers using the results of three observational runs at yearly intervals with the 43 m and 13.7 m telescopes at Green Bank, USA and Delingha, China. It is found that the masers can be divided into two types. A small majority (Type A) shows alternation of structures, caused by the existence of several unresolved maser knots within the observing beam, with the LSR velocity offset dV restricted by the simple motion of the common exciting source. The rest (Type B) show large velocity differences DV between the epochs, indicating overall motion of the ensemble of knots. Acceleration of the exciting source and the pumping mechanism are involved in the latter type.

WSRT and VLA Observations of the 6 Centimeter and 2 Centimeter LInes of H 2CO in the Direction of W3

view Abstract Citations (8) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS WSRT and VLA Observations of the 6 Centimeter and 2 Centimeter LInes of H 2CO in the Direction of W3 Dickel, Helene R. ; Goss, W. Miller ; Condon, G. R. Abstract Formaldehyde absorption toward the H ii regions in W3 has been imaged at 6 cm with the Westerbork Synthesis Radio Telescope and at 2 cm with the Very Large Array with an angular resolution of ∼5" and a velocity resolution of ∼0.6 km s-1. The opacities in both transitions are low, ranging between 0.05 and 0.3. The LSR velocities are around -39 km s-1 toward the eastern component of the molecular core which includes the H II regions W3 A and W3 B and between -45 and -42 km s-1 toward the western component which includes W3 C and W3 D. The typical line widths are 1-3 km s-1 except toward the H II region W3 D (FWHM ∼5 km s-1). For this source, a "champagne flow" at the edge of the molecular cloud may explain both the wide formaldehyde lines and the gradient in the recombination lines. Typical molecular hydrogen densities are ∼105 cm-3, in agreement with earlier estimates from observations of other molecules. The abundance of formaldehyde relative to molecular hydrogen is (1-2) × 10-9 except toward W3 D where it is ≥5 × 10-9d . The formaldehyde absorption toward the shell-like H II region W3 A is strongest toward the south/ southwest edge of the continuum source and appears to arise from a thin, compressed layer. This layer may have been compressed by the expansion of the ionized gas into part of the eastern molecular core. Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177004 Bibcode: 1996ApJ...460..716D Keywords: ISM: H II REGIONS; ISM: ABUNDANCES; ISM: INDIVIDUAL ALPHANUMERIC: W3; ISM: MOLECULES; RADIO LINES: ISM full text sources ADS | data products SIMBAD (9)

A CATALOG OF THE YOUNGEST YSOS AND CANDIDATE PROTOSTARS

ABSTRACT We have compiled a catalog of candidate protostars from the major astronomical journals up to the end of 1993. The Beichman-Ichikawa color criterion was used as the main test of an author's claim that a source should be deemed a candidate protostar. Names, positions (1950 and 2000), LSR velocities, information on whether there are associated outflows, and references are provided. This catalog is meant to update an earlier compilation by Wynn-Williams (1982).

An extremely high velocity multipolar outflow around IRAS 20050 + 2720

view Abstract Citations (50) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Extremely High Velocity Multipolar Outflow around IRAS 20050+2720 Bachiller, R. ; Fuente, A. ; Tafalla, M. Abstract We report high angular resolution maps in the CO 2 approaches 1 and CS 3 approaches 2 lines of the molecular gas around the embedded object IRAS 20050+2027. This is a 260 solar luminosity source located in the Cygnus Rift at 700 pc from the Sun. The CS data uncover a dense core of size 0.3 pc and 80 solar mass centered on the IRAS object. The CO map reveals a remarkable molecular outflow consisting of three pairs of lobes emanating from the close vicinity of the IRAS source. One of the lobe pairs is a highly collimated jet of extremely high velocity emission (LSR velocities up to +/- 70 km/s) containing molecular 'bullets'. We briefly examine different possibilties to explain the complex structure of the multipolar outflow. A single outflow appears unable to explain all the CO observations, so we suggest that two or three independent outflows emanate form different young sources embedded within the core. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/187887 Bibcode: 1995ApJ...445L..51B Keywords: Astronomical Spectroscopy; Emission Spectra; Infrared Astronomy; Interstellar Matter; Line Spectra; Molecular Flow; Molecular Gases; Spectrum Analysis; Star Formation; Cygnus Constellation; High Resolution; Infrared Astronomy Satellite; Radiation Sources; Radio Spectra; Stellar Luminosity; Astrophysics; ISM: JETS AND OUTFLOWS; ISM: INDIVIDUAL ALPHANUMERIC: IRAS 20050; 2027; ISM: MOLECULES; RADIO LINES: ISM; STARS: FORMATION full text sources ADS | data products SIMBAD (15)

Three millimeter molecular line observations in Sagittarius B2. 1: Full synthesis mapping study of HNO, CCS, and HC(13)CCN

We present the first full synthesis maps of the small molecules HNO, CCS, and HC(13)CCN in Sgr B2. We have observed the 3.8 mm continuum, the HNO J(sub K(sub -1)K(sub 1)) = 1(sub O1)-0(sub OO), the CCS J(sub N) = 7(sub 6)-6(sub 5), and the HC(13)CCN J = 9-8 transitions in the core of the Sgr B2 molecular cloud, using the Berkeley Illinois Maryland Association (BIMA) millimeter array and the NRAO 12 m telescope. We have found that HNO exists in five major gas clumps in the Sgr B2 region, which we have labeled HNO(N), HNO(NW), HNO(E), HNO(M), and HNO(S). Of particular interest is HNO(M), a major molecular gas concentration approximately 15 sec west of Sgr B2(M) in a region of young star formation. HNO is found to be closely associated with the ionized gas and might be depleted around bright H II complexes. In general, the peak intensity of the HNO emission is found to be offset from the peak of the continuum emission. We found evidence for some chemical differentiation among the three species, HNO, CCS, and HC(13)CCN, but the abundance ratios are in fair agreement with theoretical models. Two unidentified lines, U81420 and U81518, were observed, and a previously unknown compact dust source was detected. Our HNO data indicate the presence of a rotating approximately (2.2-4.4) x 10(exp 3)solar mass gas envelope surrounding Sgr B2(N), a possible bipolar gas outflow in HNO(M), and possibly a large (approximately 4.2 x 10(exp 4)solar mass) extended rotating disk associated with HNO(S). In addition, the CCS and HC(13)CCN data approximately outline the extended component of Sgr B2 and clearly show that the southern continuum source Sgr B2(S) is actually a major molecular source as well. Consequently, the kinematics of the Sgr B2 molecular cloud is quite complex, but in moving from the northwest to south, the LSR velocity generally changes from 79 to 46 km/s.

Gas kinematics and ionization along the extended sight line to HD 116852

We present Goddard High-Resolution Spectrograph intermediate observations of the interstellar medium toward HD 116852, a low halo star at a distance of 4.8 kpc (z = -1.3 kpc) in the direction l = 304. deg 9, b = 16.deg 1. The small science aperture observations have signal-to-noise ratios ranging from 30 to 90 and resolutions of 11 to 18 km/s (FWHM). We confirm the optical MK classification of this star through an analysis of its ultraviolet photosperic and stellar wind profiles. We detect interstellar lines of Al III, Si IV, C IV, and N V together with lines of C I, C I*, C I**, Si II, Ge II, P II, and Ni II. We convert the Mg II, P II, S II, Al III, Si IV, C IV, and N V profiles into measure of apparent column density as a function of LSR velocity. Gas scale height, velocity dispersion, and differential Galactic rotation effects govern the profile shapes. A simple computer model of the expected sight line column density profiles for the low and high ion species indicates that the gas velocity dispersions and scale heights increase as the ionization level of the gas increases. We find scale heigts H greater than or = 1 kpc for the high ions, which are comparable to the z-distance of the star, whereas we find H approximatley = 0.6 to 0.7 kpc for A1 III and H approximatley 0.1 kpc for P II and Ge II. An enhancement in the Al II profile near -15 km/s accounts for approximately 25% of the A1 III column along the sight line and probably arises within gas located approximately 500 pc below the Sagittarius-Carina spiral arm link. Portions of the broad underlying A1 III distribution are associated with the higher ionization lines, perhaps in conductive interfaces. The presence of N V and the column density ratios of Si IV, C IV, and N V favor the interpretation that much of the high ion absorption is produced by collisional ionization in gas with T = 1-3 x 10(exp 5) K. An enhancement near -35 km/s in both the Si IV and C IV profiles may be due to an outflow from the Norma spiral arm at a z-distance of about -1 kpc. The smooth decrease of the N(C IV)/N(Si IV) ratio at negative velocities may be due to an ISM ionization structure for hot gas that changes distance from the Galactic plane or to a two phase gas distribution in which the relative contribution from each phase changes with distance from the Galactic plane.

Composition of interstellar clouds in the disk and halo. 2: Gamma[SUP]2[/SUP] Velorum

High-resolution observations of gamma(sup 2) Vel with the Goddard High-Resolution Spectrograph (GHRS) echelle on the Hubble Space Telescope reveal the presence of seven narrow absorption components, with LSR velocities between -23 and +9 km s(exp -1). Three of these show column density ratios N(S(++))/N(S(+)) and N(P(++))/N(P+)) of about 1 or more, and can be identified as H II regions, while the other four are H I regions, consistent with the O I profile and with the overall H(sup 0) column density of 5.9 x 10(exp 19) cm(exp -2), given the usual assumptions that S is undepleted while O has a depletion D(O) = -0.3 dex. The depletions of Fe, Si, and Mn, which could be measure accurately for two of the four H I regions (components 6 and 7), differ somewhat from the values of D(sub ws) found for slowly moving warm clouds in HD 93521; in particular, for the component at 4.0 km s(exp -1) (No. 6), abosolute of D exceeds absolute of D(sub ws) by 0.1-0.4 dex, while for that at 9.3 km s(exp -1) (No. 7), absolute of D equals absolute of D(sub ws) on the average. The observed ratio of Fe + Mg atoms to Si atoms in the grains of component 6 is 2.04 +/-0.10, consistent with an olivine grain composition; the Fe/Mg ratio is 1.5 +/- 0.2. The electron density in component 6, determined from the C II(sup *) feature, is 0.075 +/- 0.013 cm (exp -3), about two-thirds of that found for clouds of this velocity in HD 93521. In the two conspicuous H II regions, components 3 and 4, n(sub e), determined from the Si II(sup *) feature, is about 1 cm(exp -3). From the column density of S(+) + S(++) in these two components, the total H II path length is about 40 pc. With the radius of a wind-blown bubble around gamma(sup 2) Vel set equal to 60 pc, the effective Stromgren radius is about 100 pc, requiring that T approx. equal to 50,000 K for the Wolf-Rayet component of the gamma(sup 2) Vel binary. Since zeta Pup is a comparable source of ionizing radiation, this temperature is an upper limit. The profiles of the strongest H2 absorption features, from Copernicus archives, indicate that the absorbing molecules have a mean velocity identical with that of the strongest H II component (No. 4). We have no explanation for the possible presence of these H2 molecules in a region of ionized H. Alternatively, the H2 profiles can be explained by molecules in the two adjacent (in velocity) H I regions, components 2 and 5, provided their H I gas has densities and temperatures typical of normal cold clouds. The GHRS data show absorption by highly ionized atoms Si(3+) and C(3+), N(4+) in broad features, in addition to the narrow-line absorption by Si(3+) and C(3+) observed in the dominant H II components, Nos. 3 and 4. The broad C(3+) and N(4+) features have widths corresponding to T in the range (4-8) x 10(exp 5) K, consistent with the broad O(5+) line shown in Copernicus data. Despite some observational uncertainties, the ratios of column densities in the broad C(3+), N(4+), and O(5+) features agree to +/- 0.1 dex with theoretical values for warm gas, heating and evaporating by thermal conduction from an adjacent hot region. Outward evaporation from an isolated cloud in a hot ambient gas cannot be distinguished, on the basis of these data, from inward evaporation of a warm shell, compressed by an expanding, hot stellar-wind bubble. For several halo stars, the C IV/O VI ratio has a quite different average value, perhaps consistent with cooling of infalling hot gas instead of conductive heating and evaporation.

Probing the galactic disk and halo. 1: The NGC 3783 sight line

We report a study of Galactic disk and halo absorption toward the Seyfert galaxy NGC 3783 which has Galactic coordinates l = 287.46 and b = +22.95. The data were obtained with the Goddard High Resolution Spectrograph operating at medium resolution with the Large Science Aperture, which produces a line spread function having a sharp core (full width at half maximum (FWHM) approximately 20 km/s) and broad wings extending to +/- 70 km/s. Ion species detected in absorption near zero LSR velocity include C IV and N V for high ions, and C I, Mg II, Si II, and S II for low ions. Absorption from a high-velocity cloud (HVC) at a velocity of +240 km/s along the sight line is also detected in the ion species of S II, Si II, and probably C I. This is the first reported case where S II and C I absorption has been detected in a HVC. The S II lines are especially useful since metal abundance estimates based on S are largely unaffected by dust grains. The study is aided by the availability of 21 cm emission data.

Water masers in the direction of the galactic center. 1: Results from initial observations

view Abstract Citations (28) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Water Masers in the Direction of the Galactic Center. I. Results From Initial Observations Taylor, Gregory B. ; Morris, Mark ; Schulman, Eric Abstract We present preliminary results from a search for water masers in the inner 4 deg x 4 deg of the Galaxy using the Very Large Array (VLA). Of 97 IRAS-selected sources observed, we report the detection of 30 H2O masers (31%). Five of these sources had previously been detected as H2O masers, six are known OH/IR stars, and one is a known SiO maser. On the basis of their infrared colors, and their H2O spectra, we categorize 14 sources as in star forming regions, 13 sources as circumstellar masers, and 3 as unknown. Seven H2O masers have been found with LSR velocities exceeding 30 km/s, indicating that they are located in the Galactic Center region. The fact remains that relatively few H2O masers have been found in the inner few hundred parsecs of the Galaxy in spite of the large concentration of molecular gas in this region. Publication: The Astronomical Journal Pub Date: November 1993 DOI: 10.1086/116779 Bibcode: 1993AJ....106.1978T Keywords: Herbig-Haro Objects; Molecular Gases; Radio Sources (Astronomy); Star Formation; Stellar Cores; Stellar Luminosity; Water Masers; Infrared Spectra; Late Stars; Radio Emission; Radio Telescopes; Very Large Array (Vla); Astrophysics; MASERS; GALAXY: CENTER full text sources ADS | data products SIMBAD (32)

Observations of Nearby Interstellar Gas and Dust in the Direction toward the Globular Cluster omega Centauri

High-resolution spectra of Na I D interstellar lines are presented for six stars which lie within 4°.0 of the globular cluster ω Centauri and at distances in the approximate range 100-600 pc. For one star (HD 116226) we discuss also the Ca II K line profile and spectra obtained with IUE. Sky flux images of the ω Cen field show considerable structure in the dust emission, and they reveal IR emission associated with faint nebulosity detected in the optical region. The spectral observations reveal gas components having negative LSR velocities between about −11 and −7 km s −1 and, in general, stronger positive velocity features between about 0.5 and 4.0 km s −1

Fragmentation and kinematics of the W49N cloud core

view Abstract Citations (60) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fragmentation and Kinematics of the W49N Cloud Core Serabyn, E. ; Guesten, R. ; Schulz, A. Abstract A multitransitional study of the W49N molecular cloud core has been carried out in seven rotational lines of CS and C(S-34), ranging in excitation from J = 3-2 to J = 10-9. The cloud core has been found to consist primarily of three dense molecular clumps, of size 0.4-1.0 pc, located approximately along an axis at P.A. 56 deg on the plane of the sky. The clumps' local densities are 2-6 x 10 exp 6/cu cm, and their masses a few 10 exp 4 solar masses each, yielding a total core mass of about 10 exp 5 solar masses. The two outer clumps are receding from us at an LSR velocity of 12 km/s, but the central clump is instead moving away at only 4 km/s, indicating that two different molecular clouds are present toward W49A. Absorption studies place the 12 km/s gas closer to us than the 4 km/s gas, implying that these two molecular clouds are converging upon each other. In addition, the central CS clump is found to be spinning rapidly in a direction counter both to Galactic rotation and to the direction inferred earlier from recombination line observations of the W49A compact H II regions. The hypothesis of global molecular cloud collapse is inconsistent with our new molecular line data. Instead, the molecular gas kinematics suggest that the enhanced O-star formation rate in W49N has been triggered by a cloud-cloud collision. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/173026 Bibcode: 1993ApJ...413..571S Keywords: Mass Distribution; Molecular Clouds; Molecular Spectra; Star Formation; Astronomical Models; Astronomical Spectroscopy; Electron Transitions; Emission Spectra; Astrophysics; ISM: INDIVIDUAL ALPHANUMERIC: W49; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES; RADIO LINES: ISM; STARS: FORMATION full text sources ADS | data products SIMBAD (3)