68 research outputs found
The young stellar population of NGC 4214 as observed with HST. I. Data and methods
We present the data and methods that we have used to perform a detailed
UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using
multifilter HST/WFPC2+STIS photometry. We explain the process followed to
obtain high-quality photometry and astrometry of the stellar and cluster
populations of this galaxy. We describe the procedure used to transform
magnitudes and colors into physical parameters using spectral energy
distributions. The data show the existence of both young and old stellar
populations that can be resolved at the distance of NGC 4214 (2.94 Mpc) and we
perform a general description of those populations.Comment: 33 pages, 9 figures, and 8 table
The young stellar population of NGC 4214 as observed with HST. II. Results
We present the results of a detailed UV-optical study of the nearby dwarf
starburst galaxy NGC 4214 using multifilter HST/WFPC2+STIS photometry. The
stellar extinction is found to be quite patchy, with some areas having values
of E(4405-5495)< 0.1 mag and others, associated with star forming regions, much
more heavily obscured, a result which is consistent with previous studies of
the nebular extinction. We determined the ratio of blue-to-red supergiants and
found it to be consistent with theoretical models for the metallicity of the
SMC. The stellar IMF of the field in the range 20-100 solar masses is found to
be steeper than Salpeter. A number of massive clusters and associations with
ages between a few and 200 million years are detected and their properties are
discussed.Comment: 49 pages, 12 figures, 6 table
Detecting metrologically useful entanglement in the vicinity of Dicke states
We present a method to verify the metrological usefulness of noisy Dicke states of a particle ensemble with only a few collective measurements, without the need for a direct measurement of the sensitivity. Our method determines the usefulness of the state for the usual protocol for estimating the angle of rotation with Dicke states, which is based on the measurement of the second moment of a total spin component. It can also be used to detect entangled states that are useful for quantum metrology. We test our approach on recent experimental results
Correlation of the Thanetian-Ilerdian turnover of larger foraminifera and the Paleocene-Eocene thermal maximum: confirming evidence from the Campo area (Pyrenees, Spain)
It has long been known that a major larger foraminifera turnover (LFT) occurred at the boundary between the Thanetian and Ilerdian stages, but its possible correlation with the Paleocene-Eocene thermal maximum (PETM) was unsuspected until the work of Baceta (1996), and has been controversial ever since. After summarizing the history of this controversy, we present information from three new sections that conclusively resolve the issue, all of them placed less than 2 km to the east of the classical Campo section in the southern Pyrenees. In these three sections, an up to 7 meter-thick intercalation of continental deposits rich in pedogenic carbonate nodules is sandwiched between uppermost Thanetian and lowermost Ilerdian shallow marine carbonates. The d13C composition of 42 pedogenic nodules collected from two of these sections (San MartĂn and La Cinglera) ranges between â11.4 and -14.3â° and averages â12.9â°, values that conclusively represent the PETM and for the first time are recorded in sections where the LFT is clearly represented. Further, a high-resolution lithological correlation between Campo and the three new sections across the P-E interval unquestionably demonstrates that the lowermost marine beds with autochthonous specimens of Alveolina vredenburgi (a tell-tale of the LFT) are laterally interfingered âand are therefore coeval- with the nodule-bearing PETM continental deposits. On the basis of the new evidence, the temporal coincidence of the PETM and the LFT can no longer be doubted
New Wolf-Rayet Galaxies with Detection of WC Stars
We report the discovery of two new Wolf-Rayet (WR) galaxies: Mrk~1039, and
F082082816. Two broad WR bumps at 5808\AA~ and 4650\AA~ indicate the
presence of WCE and WNL star population in all two sources. We also confirm the
presenceof WR features in Mrk~35, previously detected in a different position.
The observed equivalent width of the WR bump at 4650\AA~ and the derived number
ratios of WR/(WRO) imply that star formation in these sources takes place
inshort burst duration. Comparisons with the recent models of WR populations in
young starbursts with the observed EW(\HeII)/EW(\CIV)/EW(WRbump) and their
relative intensitie provide an indication that the stellar initial mass
function in some WR galaxies might not be Salpeter-like. It is interesting to
find that the luminous IRAS source, F082082816, has little dust reddening,
probably because of the existence of a powerful superwind. By comparisons with
other starbursts observed with the Hopkins Ultraviolet Telescope, F082082816
as a merging system renders a chance to study the contribution from young
starbursts to the UV background radiation in universe.Comment: 22 pages, 6 figures, 4 tables, accepted by The Astrophysical Journa
Spectrophotometric Observations of Blue Compact Dwarf Galaxies: Mrk 370
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy (BCD) Mrk 370, based on deep UBVRI broad-band and Halpha
narrow-band observations, and long-slit and two-dimensional spectroscopy of its
brightest knots. The spectroscopic data are used to derive the internal
extinction, and to compute metallicities, electronic density and temperature in
the knots. By subtracting the contribution of the underlying older stellar
population, modeled by an exponential function, removing the contribution from
emission lines, and correcting for extinction, we can measure the true colors
of the young star-forming knots. We show that the colors obtained this way
differ significantly from those derived without the above corrections, and lead
to different estimates of the ages and star-forming history of the knots. Using
predictions of evolutionary synthesis models, we estimate the ages of both the
starburst regions and the underlying stellar component. We found that we can
reproduce the colors of all the knots with an instantaneous burst of star
formation and the Salpeter initial mass function with an upper mass limit of
100 solar masses. The resulting ages range between 3 and 6 Myrs. The colors of
the low surface brightness component are consistent with ages larger than 5
Gyr. The kinematic results suggest ordered motion around the major axis of the
galaxy.Comment: 26 pages with 14 figures; accepted for publication in Ap
A Galactic O-Star Catalog
We have produced a catalog of 378 Galactic O stars with accurate spectral
classifications which is complete for V<8 but includes many fainter stars. The
catalog provides cross-identifications with other sources; coordinates
(obtained in most cases from Tycho-2 data); astrometric distances for 24 of the
nearest stars; optical (Tycho-2, Johnson, and Stromgren) and NIR photometry;
group membership, runaway character, and multiplicity information; and a
web-based version with links to online services.Comment: 76 pages, 13 tables, and 3 figures. Accepted for publication in
Astrophysical Journal. Online version of the catalog available at
http://www.stsci.edu/~jmaiz/GOSmain.htm
Redefinition of the Ilerdian Stage (early Eocene)
The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FOâs of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a chronostratigraphic subdivision of the early Eocene in a regional context. However, in addition to the paleontological criteria, the definition of the Ilerdian was also based on the designation of two reference sections in the southern Pyrenees: Tremp (stratotype) and Campo (parastratotype). In both sections, the base of the stage was placed at the lowest marine bed containing A. vredenburgi specimens. Using the CIE as a correlation tool we demonstrate that these two marine beds occur at different chronological levels, being older in Campo than in Tremp. Further, we show that both beds are in turn younger than the lowest strata with Ilerdian larger foraminifera at the deep-water Ermua section in the Basque Basin (western Pyrenees). Since the age of stage boundaries must be the same everywhere, the choice of these stratotype sections was misleading, since in practice it resulted in the Ilerdian being used as a facies term rather than as a chronostratigraphic unit. To eliminate that conflict, and yet be respectful with established tradition, we propose to redefine the Ilerdian Stage following a procedure similar to the one used by the International Commission on Stratigraphy to establish global chronostratigraphic standards, namely: by using a âsilver spikeâ to be placed in the Tremp section at the base of the Claret Conglomerate, a widespread lithological unit that in the Tremp Graus Basin coincides with the onset of the CIE. The redefined regional Ilerdian Stage becomes thus directly correlatable to the lower part of the global Ypresian Stage, as currently defined by the International Commission on Stratigraphy
The Dwarf Irregular/Wolf-Rayet Galaxy NGC4214: I. A New Distance, Stellar Content, and Global Parameters
We present the results of a detailed optical and near-IR study of the nearby
star-forming dwarf galaxy NGC4214. We discuss the stellar content, drawing
particular attention to the intermediate-age and/or old field stars, which are
used as a distance indicator. On images obtained with the Hubble Space
Telescope WFPC2 and NICMOS instruments in the equivalents of the V, R, I, J and
H bands, the galaxy is well resolved into stars. We achieve limiting magnitudes
of F814W ~27 in the WF chips and F110W ~25 in the NIC2. The optical and
near-infrared color-magnitude diagrams confirm a core-halo galaxy morphology:
an inner high surface-brightness young population within ~1.5' (~1 kpc) from
the center of the galaxy, where the stars are concentrated in bright complexes
along a bar-like structure; and a relatively low-surface-brightness, field-star
population extending out to at least 8' (7 kpc). The color-magnitude diagrams
of the core region show evidence of blue and red supergiants, main-sequence
stars, asymptotic giant branch stars and blue loop stars. We identify some
candidate carbon stars from their extreme near-IR color. The field-star
population is dominated by the "red tangle", which contains the red giant
branch. We use the I-band luminosity function to determine the distance based
on the tip-of-the-red-giant-branch method: 2.7\pm0.3 Mpc. This is much closer
than the values usually assumed in the literature, and we provide revised
distance dependent parameters such as physical size, luminosity, HI mass and
star-formation rate.Comment: 24 pages, 19 figures, accepted for publication in the July 2002 issue
of AJ. Version with high resolution figures is available at
http://www.astro.spbu.ru/staff/dio/preprints.htm
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