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At least 91 records · Page 5
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NASA NTRS1994

Multi-wavelength study of NGC 281 A

We present a study of the molecular cloud NGC 281 A and the associated compact and young star cluster NGC 281 (AS 179). Optical photometry leads to a new distance of 3500 pc for the star cluster which is in good agreement with the kinematical distance of the adjacent molecular cloud NGC 281 A. The exciting star HD 5005 of the optical nebulosity is a Trapezium system with O6 III as photometric spectral type for the component HD 5005 AB. For the age of the star cluster we estimated a value of about 3 x 10(exp 6) yr. The (12)CO (2 to 1), (13)CO (2 to 1), and (12)CO (3 to 2) emission shows that the molecular cloud NGC 281 A consists of two cloud fragments. The western fragment is more compact and massive than the eastern fragment and contains an NH3 core. This core is associated with the IRAS source 00494+5617, an H2O maser, and 1.3 millimeter dust continuum radiation. Both cloud fragments contain altogether 22 IRAS point sources which mostly share the properties of young stellar objects. They have luminosities between 150 and 8800 solar luminosity. The maxima of the 60 and 100 micrometers HIRES maps correspond to the maxima of the (12)CO (3 to 2) emission. The NGC 281 A region shares many properties with the Orion Trapezium-BN/KL region the main differences being a larger separation between the cluster centroid and the new site of star formation as well as a lower mass and luminosity of the molecular cloud and the infrared cluster.

Henning, TH.↗
DOE OSTI2026

Joint Modeling of GD-1 and C-19 as Old Streams

DESI observational data for the GD-1 and C-19 streams are compared to stream simulations in a common evolving multi-halo potential of a Milky Way-like galaxy based on a cosmological simulation. The goal is to find the best match of the stream velocity spread and the density power spectrum stream density to simulations having either CDM or WDM subhalos. The cocoon velocity width integrated over the length of the stream is independent of orbital blurring along the stream and the power spectrum integrates over the width of the stream, sidestepping the geometric details of the streams. Streams develop from star clusters inserted at $\simeq$1 Gyr after the Big Bang and evolved for 13 Gyr to their current orbital positions. Streams in a CDM subhalo population provide the best match to the velocity width, with streams younger than 10 Gyr ruled out as insufficiently hot. The progenitor star cluster masses, which determine the fraction of stars released at late times which comprise the stream core, are found to be $\simeq 8\times 10^4 M_\odot$ for GD-1 and $\simeq 4\times 10^4 M_\odot$ for C-19, although the mass depends on the star cluster half mass radius. Stream heating leads to stream lumpiness which is measurable for the relatively large and clean GD-1 dataset. The stream density power spectrum measured along the length of the DESI GD-1 sample is in good agreement with CDM simulations, with 1.7 to 1.9 times more power than WDM 7 keV and 5.5 keV simulations.

Carlberg, Raymond G. [Toronto U.] (ORCID:000000027↗
NASA NTRS1993

CCD photometry of Andromeda IV - Dwarf irregular galaxy or M31 open cluster?

CCD photometry of Andromeda IV was obtained during discretionary time in August of 1989 at the Canada-France-Hawaii Telescope on Mauna Kea and the data were reduced at CFHT during the summer of 1991. And IV has been catalogued both as a dwarf galaxy and as an open star cluster in M31. The color-magnitude diagrams presented indicate that this object has a young population of stars with a narrow age range, consistent with the characteristics of an open star cluster or stellar association. A radial velocity measurement taken from the literature and analyzed with respect to the rotation curve of M31 indicates this object resides in the disk of the Andromeda Galaxy, strengthening the conclusion that it is indeed a very large open star cluster or a densely populated stellar association rather than a dwarf irregular galaxy.

Jones, Joseph H.↗
NASA NTRS1978

Unusual satellite data: A black hole?

Data obtained by the NASA-launched European Space Agency's International Ultraviolet Explorer satellite suggests the possibility of a massive black hole at the center of some globular clusters (star groups) in our galaxy. Six of these clusters, three of them X-ray sources, were closely examined. Onboard short wavelength UV instrumentation penetrated the background denseness of the clusters 15,000 light years away where radiation, probably from a group of 10 to 20 bright blue stars orbiting the core, was observed. The stars may well be orbiting a massive black hole the size of 1,000 solar systems. The existence of the black hole is uncertain. The dynamics of the stars must be studied first to determine how they rotate in relation to the center of the million-star cluster. This may better indicate what provides the necessary gravitational pull that holds them in orbit.

Source record↗
NASA NTRS1987

Molecular gas in the starburt nucleus of M82

The 7" resolution CO observations of the central 1 kpc of M82 have resolved 2 components of molecular gas: (1) a high concentration in the central 700 pc x 200 pc, and (2) extended features that may be gas expelled from the central concentration. The central concentration of molecular gas falls in the same confines as the other tracers of recent star formation, and may be identified directly with the star burst region. The molecular gas in the star burst nucleus of M82 appears to be highly disturbed and has high kinetic temperature, likely consequences of the high density of young star clusters. Stellar winds and subsequent supernovae from the star clusters can effectively sweep up the interstellar medium. The spatial distribution and kinematics of the nuclear concentration of the molecular gas, as well as the 2 micron light distribution, suggest the presence of a stellar bar in M82. Comparisons of the M82 star burst nucleus to a sample of IR luminous galaxies suggest that star burst regions in general may have a higher gas temperature and much higher L sub IR/M sub H2 that the galactic disk, and that the L sub IR of the star burst regions may be essentially proportional to their area.

Lo, K. Y.↗
NASA NTRS1993

Radial distribution of metallicity in the LMC cluster systems

New determinations of the deprojected distances to the galaxy center for 94 star clusters and their metal abundances are used to investigate the variation of metallicity across the two LMC star cluster systems (Kontizas et al. 1990). A systematic radial trend of metallicity is observed in the extended outer cluster system, the outermost clusters being significantly metal poorer than the more central ones, with the exception of six clusters (which might lie out of the plane of the cluster system) out of 77. A radial metallicity gradient has been found, qualitatively comparable to that of the Milky Way for its system of the old disk clusters. If the six clusters are taken into consideration then the outer cluster system is well mixed up to 8 kpc. The spatial distribution of metallicities for the inner LMC cluster system, consisting of very young globulars does not show a systematic radial trend; they are all metal rich.

Kontizas, M.↗
NASA NTRS1996

IC 1257: A New Globular Cluster in the Galactic Halo

New CCD photometry of the faint, compact star cluster IC 1257 (L = 17? = +/- 15?obtained with the Palomar 5m telescope, reveals that it is a highly reddened globular cluster well beyond the Galactic center.

ccd photometry stars clusters star cluster globula↗
NASA NTRS1995

Map-based trigonometric parallaxes of open clusters: Coma

This is the fourth study in a series to determine the direct trigonometric parallaxes of four of the nearest open star clusters, the Hyades, the Pleiades, the Praesepe, and the nearby cluster in Coma (Gatewood et al. 1990; Gatewood et al. 1992); Gatewood & Kiewiet de Jonge 1994). The results for the open star cluster in Coma are compared with those of the other three clusters, and the members are found to be significantly subluminous. The trigonometric parallax of the cluster is estimated from that of three members studied with the Multichannel Astrometric Photometer (MAP) at the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of the cluster is +13.53 +/- 0.54 mass (0.00054 min), corresponding to a distance modulus of 4.34 +/- 0.09 mag. The U-B excess of the Coma cluster members may be used to adjust the observed absolute magnitudes and the B-V measurements as suggested by Sandage & Eggen (1959). The agreement obtained in this manner suggests that, like subdwarf stars, the stars of the Coma cluster appear subluminous because of line blanketing. One of the three members observed in this study was recognized as a member by its parallax and is the faintest known member of the cluster.

Gatewood, George↗
NASA NTRS1994

Hubble Space Telescope imaging of the central star forming region in NGC 1140 (exp 1)

We present broadband images taken with the Hubble Space Telescope's Planetary Camera of the central supergiant H II region in the amorphous galaxy NGC 1140. These images allow observations to a resolution of about 13 pc at the galaxy, and they reveal that its central 1/2 kpc contains 6-7 blue, luminous, compact super star clusters, many of which would be comparable in luminosity to globular clusters at the same age. A blue arc-shaped structure near the center may be a grouping of less luminous, R136/NGC 2070-sized clusters or a sheet of OB stars. Additional somewhat less luminous and redder clusters are also found farther out from the center. If these clusters are older, they too could have had luminosities comparable to those of the central six clusters at a comparable age. Thus, we find that NGC 1140 is remarkable in the number of extreme clusters that it has formed recently in a relatively small area of the galaxy. Since NGC 1140 exhibits global characteristics that are consistent with a recent merger, these clusters are likely to be a product of that event. This galaxy adds to the number of cases where rapid star formation has evidently produced super star clusters.

Hunter, Deidre A.↗
DOE OSTI2026

Discovery and Spectroscopic Characterization of a Distant, Compact Milky Way Satellite in Gemini

We present the discovery of a compact Milky Way satellite in the constellation of Gemini. This system was discovered by cross-matching detections from two independent search algorithms applied to Blanco/DECam data from the third data release of the DECam Local Volume Exploration survey (DELVE DR3), and confirmed with deeper imaging from Gemini/GMOS-N. Based on these data, we determine that the system is an ultra-faint ($M_V = -2.1^{+0.4}_{-0.6}$), compact ($r_{1/2} = 8.6^{+1.4}_{-1.2}$ pc) system located at a heliocentric distance of $120^{+7}_{-6}$ kpc. These physical properties place the system in the regime of ambiguous, ultra-faint compact Milky Way halo satellites that cannot be confidently classified as dwarf galaxies or star clusters from morphology alone; we therefore name the system DELVE 8/Gemini I. From medium-resolution Keck/DEIMOS spectroscopy, we securely identify four members including two blue horizontal branch stars, confirming the system as a bound satellite moving at a mean radial velocity of $v_{\rm hel} = -82.7^{+3.7}_{-3.9} {\rm km\,s}^{-1}$. We also use these spectra to place an upper limit of $\rm [Fe/H] \lesssim -2.5$ on the metallicity of DELVE 8/Gemini I's brightest star, supporting the classification of the system as either an ancient star cluster or ultra-faint dwarf galaxy. The discovery of faint, distant systems similar to DELVE 8/Gemini I is expected to become more common with upcoming surveys.

Overdeck, K. [Chicago U., Astron. Astrophys. Ctr.;↗
NASA NTRS1990

Starburst outflows from nearby galaxies

Starburst outflows from NGC 5461, 1569 and M82 are discussed. The Sc I galaxy, M101, is reknowned for the kpc-size superassociations of star clusters and HII regions that dominate its spiral arms. NGC 5461 is one of the brightest of these superassociations, rivaling the Large Magellanic Cloud in H alpha luminosity. The NGC 5461 superassociation is dominated by a single unresolved HII region of outstanding luminosity (approx. 1000 Orion nebulae). Detailed examination of corresponding continuum images indicates that only the southern plume has any sort of stellar counterpart. The other plumes are clearly diffuse with no underlying hot stars. An image of NGC 1569 is discussed. Besides showing the peculiar arm noted by Zwicky (1971) and the filamentary extensions to the North and South (as noted by Hodge 1974), this image also reveals two arc-like features of diffuse ionized gas to the South. Both arcs are concentric with the bright center of the galaxy - where the super star clusters, A and B are located. The inner arc (Arc 1) appears to follow the same curve as the SW arm thus suggesting that the two features represent limb-brightened fragments of vast superbubble that was blown out by a central starburst sometime in the past. As the classic starburst galaxy, M82 displays all the luminous hallmarks of intense high-mass star formation and outflow activity. The diffuse H alpha and x ray emitting gas along the minor axis provides especially good evidence for a bipolar outflow of hot gas which is shock heating the swept-up interstellar medium (ISM) to temperatures of approx. 10(exp 4) K. An image shows the H alpha emission within the disk and along the minor axis. Another image shows the same field in the light of near-infrared. Both figures are based on charge coupled device images taken with the McGraw-Hill 1.3 m telescope (Waller 1989). The longer wavelength emission clearly shows a more extended morphology along the major axis. The morphological discrepancy is most likely due to the greater obscuration by dust suffered by the H alpha photons. A third image shows the map of visual extinction that researchers derive from a pixel-by-pixel comparison of the (SIII) and H alpha fluxes. The greatest extinctions are evident along an arc that includes two especially obscured regions on opposite sides of the bursting nucleus.

Waller, William H.↗
NASA NTRS1990

Ultraviolet gas absorption and dust extinction toward M8

Interstellar absorption lines are analyzed using high-resolution IUE spectra of 11 stars in the young cluster NGC 6530 located in the M8 region. High-velocity clouds at -35 km/s and -60 km/s are seen toward all cluster stars. The components arise in gases that are part of large interstellar bubbles centered on the cluster and driven by stellar winds of the most luminous members. Absorption lines of species of different ionization states are separated in velocity. The velocity stratification is best explained as a 'champagne' flow of ionized gas away from the cluster. The C IV/Si IV ratios toward the hotter cluster members are consistent with simple photoionization models if the gas-phase C/Si ratio is increased by preferential accretion onto dust grains. High ion column densities in the central cluster decline with distance from W93, suggesting that radiation from a hot source near W93 has photoionized gas in the central cluster.

Boggs, Don↗
NASA NTRS1982

Far-infrared observations of the evolved H II region M16

The results of far infrared (FIR) observations of the larger H II region M16, associated with the young open star cluster NGC 6611, are discussed. Three FIR sources detected on an extended ridge of FIR emission within the scanned region are described. The observations confirm that M16 is an H II region in a late stage of evolution. The H II region has expanded and is now extremely density bounded, consisting of an extended region of ionized gas and a series of ionization fronts located at the surrounding molecular cloud boundaries nearest to the exciting OB star cluster. The FIR radiation arises from heated dust at these boundaries.

Mcbreen, B.↗
NASA NTRS1966

Problems of stellar dynamics

Many-body problem, continuum, and statistical methods applied to dynamics of star clusters, with bibliography

STAR CLUSTER↗
NASA NTRS1991

Close binary stars in globular clusters

Although close binary stars are thought theoretically to play a major role in globular cluster dynamics, virtually no non-degenerate close binaries are known in clusters. We review the status of observations in this area, and report on two new programs which are finally yielding candidate systems suitable for further study. One of the objects, a close eclipsing system in omega Cen, is also a big straggler, thus finally proving firm evidence that globular cluster blue stragglers really are binary stars.

Margon, Bruce↗
NASA NTRS1989

The detection of an IR excess toward the globular cluster RV Tauri variable M28 V17

The paper presents the results of a search for IR emission excesses toward three globular cluster stars. Two of the stars are RV Tau variables (M28 V17 and M5 V85) and one is believed to be a W Vir variable (M5 V42) which is historically linked to the RV Tau class. Consideration is given to the implications of the observed detections, in particular, the establishment of M28 V17 as a star in a globular cluster that is indistinguishable from the Preston type A subclass.

Nook, Mark A.↗