Outer Galactic Disk Research Articles

Period Measurement of AGB Stars in the Outer Galactic Disk

The light variation of the 47 AGB star candidates in the outer galactic disk has been monitored at the I-band for 5 years. Periods were well determined for 18 of them, and less reliably for the other 25. The average period of the objects is then 500 days. According to the period-luminosity relation, the mean luminosity of the sample stars is 10000 L⊙. Based on the absolute luminosity, derived from the period-luminosity relation and the apparent luminosity from the observation, the distances to the objects were determined. The calculated distances are slightly greater than those obtained previously based on the assumption of a constant luminosity of 8000 L⊙. In addition, SiO maser emission was detected for most of the observed objects, so that their radial velocities were accurately known. With the assumption of circular rotation in galactic disk, the rotation curve and Oort's constants were derived.

SiO Masers in Stars in the Inner and Outer Galactic Disk

Observations in the J = 1–0, v = 1 and v = 2 28SiO and v = 0 29SiO maser lines were made towards 97 outer- and 19 inner-disk IRAS sources with typical IRAS colors of AGB stars. 21 new 28SiO and 1 new 29SiO maser sources were detected above the 5 σ level of ∼ 1 Jy with the Nobeyama 45 m telescope. Collecting all of the observational data in SiO J = 1–0 maser lines taken with a 45 m telescope, a comparison is made between the outer-disk, inner-disk, and bulge samples. The samples, themselves, align a sequence of mid-infrared color, flux at 12 μm and IRAS variability index. The detection rates are 66%, 51%, and 31%, respectively, in the bulge, inner disk, and outer disk. This fact is consistent with the tendency of increasing proportion of C-rich stars in the IRAS sample and metallicity gradient with the galactocentric distance.

Abundance Gradients in the Outer Galactic Disk

Radial abundance gradients of the element ratios O/H, Ne/H, S/H, and Ar/H are determined for a sample of disk planetary nebulae, emphasizing the behaviour of the gradients at large galactocentric distances.

The Extreme Outer Regions of Disk Galaxies. I. Chemical Abundances of H [CSC]ii[/CSC] Regions

?????We present the first results of an ongoing project to investigate the present-day chemical abundances of the extreme outer parts of galactic disks, as probed by the emission-line spectra of a new sample of H II regions. The galaxies studied here, NGC 628, NGC 1058, and NGC 6946, are all late-type spiral galaxies, characterized by larger than average H I?to?optical sizes. Our deep H? images have revealed the existence of recent massive star formation, traced by H II regions, out to and beyond two optical radii in these galaxies (defined by the B-band 25th magnitude isophote). Optical spectra of these newly discovered H II regions are used to investigate their densities, ionization parameters, extinctions, and, in particular, their oxygen and nitrogen abundances. Our measurements reveal gas-phase abundances of O/H ~ 10%?15% of the solar value and N/O ~ 20%?25% of the solar value at radii of (1.5?2)R25. Clear evidence also exists for diminished dust extinction (AV ~ 0?0.2 mag) at large radii. The combination of our measurements of outer disk H II region abundances with those for inner disk H II regions published in the literature is a powerful probe of the shape of abundance gradients over unprecedented radial baselines. The predictions of models of chemical evolution often diverge most strongly in the outer parts of galaxies. Both the oxygen and the nitrogen-to-oxygen abundances generally decrease with increasing radius. Within the limits of the current data set, the radial abundance variations are consistent with single log-linear relationships, although the derived slopes can often differ considerably from those found if only inner disk H II regions are used to define the fit. The small number of H II regions in our present sample, together with uncertainties in the calibrations of the empirical methods used here to determine abundances, limit the ability to constrain both subtle changes in the radial gradient and intrinsic scatter at a fixed radius. Nitrogen-to-oxygen ratios appear to be consistent with a combination of primary and secondary production of nitrogen. Interestingly, both the mean level of enrichment and the N/O ratio measured in extreme outer galactic disks are similar to those values measured in some high-redshift damped Ly? absorbers, suggesting that outer disks at the present epoch are relatively unevolved.

Observational Study of AGB Stars in the Outer Galactic Disk

Observational Study of AGB Stars in the Outer Galactic Disk

SiO Maser Sources in the Outer Disk of the Galaxy

view Abstract Citations (42) References (59) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SiO Maser Sources in the Outer Disk of the Galaxy Jiang, B. W. ; Deguchi, S. ; Yamamura, I. ; Nakada, Y. ; Cho, S. H. ; Yamagata, T. Abstract The observations in the 28SiO j = 1-0 V = 1, J = 1-0 V = 2 lines and the 29SiO j = 1-0, V = 0 lines were simultaneously made toward 181 color-selected IRAS sources in the outer disk of the Galaxy (at longitudes between 90° and 250°). The 28SiO lines were detected in 63 sources (56 new) and the 29SiO line in 11 sources (9 new). Most of the detections are optically variable stars, mainly Mira-type variables and a few semiregular variables. The detection rate (35%) is much lower than that of the bulge survey performed by the same observational system the 45 m telescope at Nobeyama Radio Observatory. The lower detection rate of SiO maser emission is partly attributed to the increase of contaminations by stars with C-rich circumstellar envelopes and young stellar objects in the outer disk sample. The kinematical implications of the observational results are also discussed. The luminosity distances to the SiO maser sources are estimated from their IRAS fluxes at 12 μm and colors. By combining the SiO radial velocity and the luminosity distance, the rotation curve of the outer Galactic disk is found to be slightly falling within the Galactocentric distance between 8.5 and 12 kpc. The sources located within 20° from the Galactic anticenter direction are used to check for a peculiar motion of the local standard of rest. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1996 DOI: 10.1086/192345 Bibcode: 1996ApJS..106..463J Keywords: GALAXY: KINEMATICS AND DYNAMICS; ISM: MOLECULES; MASERS; STARS: VARIABLES: OTHER LONG-PERIOD VARIABLES full text sources ADS | data products SIMBAD (182) CDS (2) Related Materials (1) Catalog: 1997yCat..21060463J

Chemical abundances in the Outer Disk Clusters Tombaugh 2, Melotte 71, and NGC 2112

We have analyzed high-dispersion echelle spectra of two or three stars each in the old anticenter disk clusters Tombaugh 2, NGC 2112, and Melotte 71. We find all three clusters to be mildly metal deficient, with [Fe/H]≃-0.45, -0.1, and -0.3, respectively, with an error of ∼0.2 dex. The clusters also have slight overdeficiencies of oxygen and nearly solar proportions of the α elements, indicating a lower relative contribution by massive stars to the chemical evolution of the outer Galactic disk. The clusters are found to be less metal deficient than photometric and low-resolution spectroscopic studies had indicated, which we attribute to severe nonmember contamination in those samples and/or reddening uncertainties. Our analysis suggests reddening values of E(B - V) =0.3-0.4 for Tom 2 and E(B - V) ≍0.6 for NGC 2112. NGC 2112 suffers from severe field star contamination.

Optical detection of the Galaxy's southern stellar warp and outer disk

We report the probable detection of the stellar population in the outer Galactic disk in the direction of the southern Galactic warp. VI c CCD photometry was obtained for four fields toward the southern Galactic warp and four control fields at equal longitudes but opposite latitudes. All fields were chosen to have uniform star densities and galaxies visible in or very near the fields. More stars are seen in all four warp fields compared to the four control directions, and the excesses are unlikely to be caused solely by the Sun's position north of mid-plane. One warp-control field pair appear to have very similar reddening versus distance behavior, and simple subtraction of the control field from the warp field reveals a well-defined main sequence and perhaps a turnoff for the outer stellar disk

Precision photometry of young stellar groups towards the outer Galactic disk and the Galactic rotation curve

view Abstract Citations (44) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Precision Photometry of Young Stellar Groups Towards the Outer Galactic Disk and the Galactic Rotation Curve Turbide, Luc ; Moffat, Anthony F. J. Abstract We have used a CCD to obtain stellar UBV magnitudes to V = 18 towards eight distant, young stellar groups in the third Galactic quadrant where interstellar extinction is low (l = 210 deg-242 deg). Comparison with theoretical isochrones yields ages and distances of significantly improved precision compared to previous studies based on photoelectric diaphragm photometry. One of the groups (in the faint H II region S 289) is located twice as far from the Galactic center as the sun and is likely located near the outer limit of active star formation in the Galactic disk. Together with published radial velocities and allowing for a metallicity gradient, the new distances harden the evidence for a flat Galactic rotation curve out to R about 16 kpc. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116558 Bibcode: 1993AJ....105.1831T Keywords: Astronomical Photometry; Charge Coupled Devices; Color-Magnitude Diagram; Galactic Rotation; Radial Velocity; Stellar Magnitude; Faint Objects; Interstellar Extinction; Astronomy; GALAXY: STELLAR CONTENT; GALAXY: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (39)

Molecular Line Observations of the Galactic Center Region

A decade of galactic center observations at the Crawford Hill 7 m antenna is summarized. The galactic center region contains several hundred high-mass, high-density molecular clouds with physical properties very different from clouds in the outer galactic disk. There is also a considerable amount of molecular gas not bound into clouds, but sheared by differential rotation into a molecular inter-cloud medium not seen elsewhere in the Galaxy. These observations can be explained by a combination of the tidal density limit and the virial theorem. The distribution of emission on the sky and in velocity suggests that most of the dense gas is confined to a 500 pc long ridge of emission which may be a dust lane along the central bar.

A latitude survey of carbon monoxide emission near the Galactic center

view Abstract Citations (21) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Latitude Survey of Carbon Monoxide Emission near the Galactic Center Bania, T. M. Abstract A new (C-12)O survey of the inner Galaxy is reported together with some additional observations of (C-13)O in selected directions. Most of the CO emissivity in this zone could be produced by only three structures; the nuclear disk/bar, the 3 kpc arm, and the +135 km/s feature. Selected giant molecular clouds (GMCs) near the (1,v)-loci predicted by kinematic ring models for the 3 kpc and +135 km/s arms have been observed in (C-13)O in order to estimate their physical properties. Except for 10 km/s CO line widths typical of clouds near the Galactic center, these objects have properties very similar to those derived for the GMC population in the outer Galactic disk. The clouds are typically 100 pc in diameter with H2 masses of a million solar masses, and they have excitation temperatures of 7 K. Publication: The Astrophysical Journal Pub Date: September 1986 DOI: 10.1086/164558 Bibcode: 1986ApJ...308..868B Keywords: Carbon Monoxide; Emission Spectra; Galactic Nuclei; Milky Way Galaxy; Molecular Clouds; Astronomical Spectroscopy; Gas Dynamics; Spectral Line Width; Astrophysics; GALAXIES: MILKY WAY; GALAXIES: NUCLEI; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (4) NED (1)

Clump 1 - an unusual molecular cloud complex near the Galactic center

The properties of the (C-12)O and (C-13)O emission from Clump I, a complex of molecular clouds which shows the largest noncircular velocities of any molecular material known in the Milky Way, are studied. Observations of the J = 1-0 rotational transitions of the above molecules are reported, and the large-scale distribution and kinematics of the molecular gas in the direction of Clump I are discussed. The small-scale structure is described based on one arcmin resolution of (C-13)O data. Physical properties of the molecular material are derived, and the dynamics of the Clump I clouds are discussed in the context of their stability against Galactic tidal forces. It is concluded that all the clouds in the complex are gravitationally bound, although their outer envelopes may be tidally disrupted by the Galactic potential. The relative motion of the clouds is qualitatively similar to giant molecular cloud complexes in spiral arms of the outer Galactic disk, but the velocities are higher.

Remote OB stars in Puppis

view Abstract Citations (15) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Remote OB stars in Puppis. Stetson, P. B. ; Fitzgerald, M. P. Abstract Spectroscopic observations are presented for 54 remote OB stars in Puppis, for which UBV photometry has been published by Reed and FitzGerald (1983). The combination of MK spectral classification and the photometric data suggests that the overwhelming majority of these stars lie at a common distance of about 6 kpc from the sun, and may form a physical association. This result prevents using these stars to achieve the original goal of mapping the rotation curve of the outer Galactic disk. Publication: The Astronomical Journal Pub Date: June 1985 DOI: 10.1086/113813 Bibcode: 1985AJ.....90.1060S Keywords: Astrometry; B Stars; Blue Stars; O Stars; Radial Velocity; Stellar Spectra; Color-Magnitude Diagram; Distance; Star Clusters; Stellar Luminosity; Astrophysics full text sources ADS | data products SIMBAD (19) NED (1)

Effects of environment on neutral hydrogen distribution for disk galaxies in the Virgo Cluster area

A statistical analysis is carried out on H I observations of galaxies, which include mapping with the Arecibo beam (reported in previous papers), both inside and outside the direction of the Virgo cluster core (radius 5/sup 0/ or 6/sup 0/). The galaxies were classified both according to the revised Hubble (RH) scheme and the RDDO scheme suggested by van den Bergh. SO galaxies on the RH scheme have a larger detection probability outside than inside; ''true SO'' galaxies on the RDDO scheme have a small detection probability everywhere; ''anemics'' have a larger detection probability and are more common outside the cluster core. Anemic and spiral galaxies of all types have an average H I mass content M/sub H/ which is smaller inside the Virgo cluster core by a factor of about 2 to 2.5 than galaxies of the same type outside the core. This result agrees with that obtained by Chamaraux et al., using different methods, and seems now firmly established. H I diameters D/sub H/, defined in terms of a scale length, are also smaller inside the core than outside so that the surface density sigma/sub H/proportionalM/sub H//D/sub H//sup 2/ is almost the same inside and outside (always comparingmore » galaxies of the same morphological type). Ram pressure stripping of an outer galactic disk by intracluster gas predicts just such results. By contrast, ''anemics'' have almost the same D/sub H/ as a ''true spirals'' (or even larger) but smaller sigma/sub H/, suggesting they lost hydrogen gas by some means other than stripping.« less

King 8 - A metal-poor disk cluster

view Abstract Citations (15) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS King 8 : a metal-poor disk cluster. Christian, C. A. Abstract The faint cluster, King 8 (IAU designation C00546+336), was observed as part of a study of galactic anticenter stars, which are used as probes of the environmental conditions in the outer galactic disk. The distribution of stellar ages and metallicities as a function of position can be compared to the properties of solar neighborhood stars, and thereby serve as constraints for theoretical models. BV observations are considered, taking into account photoelectric data, photographic data, and video camera data. The final photographic values for all stars measured are listed in a table. Video camera magnitudes were averaged with photographic magnitudes when available. Attention is given to a color-magnitude diagram, the luminosity function, a two-color diagram, slitless spectra, and IIDS spectrophotometry. The color-magnitude diagram morphology of King 8 suggests this open cluster is a moderate age, 800 million years, metal-poor (Y = 0.30, Z = 0.01) object located in the anticenter 3-4 kpc from the sun. Publication: The Astrophysical Journal Pub Date: June 1981 DOI: 10.1086/158978 Bibcode: 1981ApJ...246..827C Keywords: Abundance; Star Clusters; Stellar Luminosity; Stellar Spectrophotometry; A Stars; Astronomical Photography; Color; Color-Magnitude Diagram; Metallic Stars; Open Clusters; Star Distribution; Stellar Evolution; Stellar Magnitude; Stellar Spectra; Astronomy full text sources ADS | data products SIMBAD (78) GCPD (1)