4,089 research outputs found
The extent of NGC 6822 revealed by its C stars population
Using the CFH12K camera, we apply the four band photometric technique to
identify 904 carbon stars in an area 28' x 42' centered on NGC 6822. A few C
stars, outside of this area were also discovered with the Las Campanas Swope
Telescope. The NGC 6822 C star population has an average I of 19.26 mag leading
to an average absolute I magnitude of
-4.70 mag, a value essentially identical to the mean magnitude obtained for
the C stars in IC 1613. Contrary to stars highlighting the optical image of NGC
6822, C stars are seen at large radial distances and trace a huge slightly
elliptical halo which do not coincide with the huge HI cloud surrounding
NGC6822. The previously unknown stellar component of NGC 6822 has a exponential
scale length of 3.0' +/- 0.1' and can be traced to five scale lengths. The C/M
ratio of NGC 6822 is evaluated to br 1.0 +/- 0.2.Comment: accepted, to be published in A
Photometric Survey of the Polar ring galaxy NGC 6822
We have previously established, from a carbon star survey, that the Local
Group dwarf irregular galaxy NGC 6822 is much larger than its central bright
core.
Four MegaCam fields are acquired to survey a 2 2 area
centred on NGC 6822 to fully determine its extent and map its stellar
populations. Photometry of over one million stars is obtained in the SDSS g,
r, i to three magnitudes below the TRGB. RGB stars, selected from their
magnitudes and colours, are used to map the NGC 6822 stellar distribution up to
a distance of 60 arcmin. We map the reddening over the whole area. We establish
that the stellar outer structure of NGC 6822 is elliptical in shape, with
and a major-axis PA = 65, contrasting with the
orientation of the HI disk. The density enhancement can be seen up to a
semi-major axis of 36 making NGC 6822 as big as the Small Magellanic Cloud.
We fit two exponentials to the surface density profile of the spheroid, and
identify a bulge with a scale length of 3.85 and an outer spheroid with a
scale length of 10.0. We find intermediate-age C stars up to 40
while demonstrating that the SDSS filters are unsuitable to identify
extragalactic C stars. NGC 6822 is a unique Local Group galaxy with shape and
structure suggesting a polar ring configuration. Radial velocities of carbon
stars have indeed demonstrated that there are two kinematical systems in NGC
6822.Comment: A&A in pres
Constraining the History of the Sagittarius Dwarf Galaxy Using Observations of its Tidal Debris
We present a comparison of semi-analytic models of the phase-space structure
of tidal debris with observations of stars associated with the Sagittarius
dwarf galaxy (Sgr). We find that many features in the data can be explained by
these models. The properties of stars 10-15 degrees away from the center of Sgr
--- in particular, the orientation of material perpendicular to Sgr's orbit
(c.f. Alard 1996) and the kink in the velocity gradient (Ibata et al 1997) ---
are consistent with those expected for unbound material stripped during the
most recent pericentric passage ~50 Myrs ago. The break in the slope of the
surface density seen by Mateo, Olszewski & Morrison (1998) at ~ b=-35 can be
understood as marking the end of this material. However, the detections beyond
this point are unlikely to represent debris in a trailing streamer, torn from
Sgr during the immediately preceding passage ~0.7 Gyrs ago, but are more
plausibly explained by a leading streamer of material that was lost more that 1
Gyr ago and has wrapped all the way around the Galaxy. The observations
reported in Majewski et al (1999) also support this hypothesis. We determine
debris models with these properties on orbits that are consistent with the
currently known positions and velocities of Sgr in Galactic potentials with
halo components that have circular velocities v_circ=140-200 km/s. The best
match to the data is obtained in models where Sgr currently has a mass of ~10^9
M_sun and has orbited the Galaxy for at least the last 1 Gyr, during which time
it has reduced its mass by a factor of 2-3, or luminosity by an amount
equivalent to ~10% of the total luminosity of the Galactic halo. These numbers
suggest that Sgr is rapidly disrupting and unlikely to survive beyond a few
more pericentric passages.Comment: 19 pages, 5 figures, accepted to Astronomical Journa
Magellanic Cloud Periphery Carbon Stars IV: The SMC
The kinematics of 150 carbon stars observed at moderate dispersion on the
periphery of the Small Magellanic Cloud are compared with the motions of
neutral hydrogen and early type stars in the Inter-Cloud region. The
distribution of radial velocities implies a configuration of these stars as a
sheet inclined at 73+/-4 degrees to the plane of the sky. The near side, to the
South, is dominated by a stellar component; to the North, the far side contains
fewer carbon stars, and is dominated by the neutral gas. The upper velocity
envelope of the stars is closely the same as that of the gas. This
configuration is shown to be consistent with the known extension of the SMC
along the line of sight, and is attributed to a tidally induced disruption of
the SMC that originated in a close encounter with the LMC some 0.3 to 0.4 Gyr
ago. The dearth of gas on the near side of the sheet is attributed to ablation
processes akin to those inferred by Weiner & Williams (1996) to collisional
excitation of the leading edges of Magellanic Stream clouds. Comparison with
pre LMC/SMC encounter kinematic data of Hardy, Suntzeff, & Azzopardi (1989) of
carbon stars, with data of stars formed after the encounter, of Maurice et al.
(1989), and Mathewson et al. (a986, 1988) leaves little doubt that forces other
than gravity play a role in the dynamics of the H I.Comment: 30 pages; 7 figures, latex compiled, 1 table; to appear in AJ (June
2000
Understanding the importance of sport stadium visits to teams and cities through the eyes of online reviewers
This study explores the relationships among sport stadium visitors’ experiences, satisfaction, team brand image, and destination image. A text mining approach was first used to analyse 26,538 individual reviews from 17 European sport stadiums on TripAdvisor. The online reviews were then used as input to create a word frequency of each individual review and construct a structural equation model. Results indicate that the visitor experience had a strong impact on team brand image and a moderate effect on destination image. Satisfaction mediated the influence of the visitor experience on team brand image, but not on destination image. Team brand image exerted a significant but small impact on destination image. These findings show that stadium visits impact the marketing of both host teams and cities. City, leisure and stadium managers should therefore coordinate their efforts to highlight teams as part of a city’s cultural brand to generate image-based benefits for both.info:eu-repo/semantics/publishedVersio
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