376 research outputs found
On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg II k
line at 2796.34 A. The work is based on a selection of 230 stars observed by
both the IUE and HIPPARCOS satellites, covering a wide range of spectral type
and absolute visual magnitudes. The Wilson-Bappu relationship here provided is
considered to represent an improvement over previous recent results for the
considerably larger data sample used as well as for a proper consideration of
the measurement errors. No evidence has been found for a possible dependence of
the WB effect on stellar metallicity and effective temperature.Comment: 8 pages, 8 figures Accepted for publication on A&
A study of the Mg II 2796.34 A emission line in late--type normal, and RS CVn stars
We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars
and make a comparison with the normal stars studied in a previous paper (Paper
I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS
parallaxes and observed at high resolution with IUE. We confirm that RS CVn
stars tend to possess wider Mg II lines than normal stars having the same
absolute visual magnitude. However, we could not find any correlation between
the logarithmic line width log Wo and the absolute visual magnitude Mv (the
Wilson--Bappu relationship) for these active stars, contrary to the case of
normal stars addressed in Paper I. On the contrary, we find that a strong
correlation exists in the (Mv, log L) plane (L is the absolute flux in the
line). In this plane, normal and RS CVn stars are distributed along two nearly
parallel straight lines with RS CVn stars being systematically brighter by
about 1 dex. Such a diagram provides an interesting tool to discriminate active
from normal stars. We finally analyse the distribution of RS CVn and of normal
stars in the (log L, log Wo) plane, and find a strong linear correlation for
normal stars, which can be used for distance determinations.Comment: 10 pages, 7 figures, latex, to be published in A&
Tumour-infiltrating lymphocytes bear the 75 kDa tumour necrosis factor receptor.
Tumour necrosis factor alpha (TNF-alpha) is a cytokine with a variety of immunological properties. The identification of two receptors for this molecule, i.e. the 75 kDa and the 55 kDa TNF receptors (TNF-R), recently clarified the mechanisms through which this cytokine provides its wide range of immunomodulatory activities. In this study we have investigated the expression and the functional properties of these receptors on tumour-infiltrating lymphocytes (TILs) recovered from 17 patients with solid cancers (melanoma, colorectal carcinoma and lung cancer). To this end, TIL lines and freshly isolated TILs were evaluated for (a) the expression and the functional role of TNF receptors following culture in the presence of interleukin 2 (IL-2) and (b) the production of TNF-alpha following culture with IL-2 and the role of this cytokine in IL-2-driven TIL proliferation. Flow cytometry analysis demonstrated that TILs bear the 75 kDa TNF-R. Moreover, TIL lines express detectable messages for TNF-alpha and release this cytokine. Functional in vitro studies have shown that anti-TNF-alpha, as well as anti-75 kDa TNF-R antibodies, are able to inhibit the IL-2-induced TIL proliferation. These data demonstrate that TILs are equipped with a fully functional TNF-R system and suggest a putative role for this receptor and its ligand in the activation and expression of TILs following immunotherapy with IL-2
Mg II h + k emission lines as stellar activity indicators of main sequence F-K stars
The main purpose of this study is to use the IUE spectra in the analysis of
magnetic activity of main sequence F-K stars. Combining IUE observations of
MgII and optical spectroscopy of Ca II, the registry of ctivity of stars can be
extended in time. We retrieved all the high-resolution spectra of F, G, and K
main sequence stars observed by IUE (i.e. 1623 spectra of 259 F to K dwarf
stars). We obtained the continuum surface flux near the Mg II h+k lines near
2800 \AA and the MgII line-core surface flux from the IUE spectra. We obtained
a relation between the mean continuum flux near the MgII lines with the colour
of the star. For a set of 117 nearly simultaneous observations of Mg II
and Ca II fluxes of 21 F5 to K3 main sequence stars, we obtained a colour
dependent relation between the Mount Wilson CaII S-index and the MgII emission
line-core flux. As an application of this calibration, we computed the Mount
Wilson index for all the dF to dK stars which have high resolution IUE spectra.
For some of the most frequently observed main sequence stars, we analysed the
Mount Wilson index S from the IUE spectra, together with the ones derived from
visible spectra. We confirm the cyclic chromospheric activity of epsilon Eri
(HD 22049) and beta Hydri (HD 2151), and we find a magnetic cycle in alpha Cen
B (HD 128621). Complete abstract in the paper.Comment: 10 pages, accepted for publication in Astronomy and Astrophysic
Modeling of the Super-Eddington Phase for Classical Novae: Five IUE Novae
We present a light curve model for the super-Eddington luminosity phase of
five classical novae observed with IUE. Optical and UV light curves are
calculated based on the optically thick wind theory with a reduced effective
opacity for a porous atmosphere. Fitting a model light curve with the UV 1455
\AA light curve, we determine the white dwarf mass and distance to be (1.3
M_sun, 4.4 kpc) for V693 CrA, (1.05 M_sun, 1.8 kpc) for V1974 Cyg, (0.95 M_sun,
4.1 kpc) for V1668 Cyg, (1.0 M_sun, 2.1 kpc) for V351 Pup, and (1.0 M_sun, 4.3
kpc) for OS And.Comment: 9 pages including 8 figures, to appear in the Astrophysical Journa
Novae Ejecta as Colliding Shells
Following on our initial absorption-line analysis of fifteen novae spectra we
present additional evidence for the existence of two distinct components of
novae ejecta having different origins. As argued in Paper I one component is
the rapidly expanding gas ejected from the outer layers of the white dwarf by
the outburst. The second component is pre-existing outer, more slowly expanding
circumbinary gas that represents ejecta from the secondary star or accretion
disk. We present measurements of the emission-line widths that show them to be
significantly narrower than the broad P Cygni profiles that immediately precede
them. The emission profiles of novae in the nebular phase are distinctly
rectangular, i.e., strongly suggestive of emission from a relatively thin,
roughly spherical shell. We thus interpret novae spectral evolution in terms of
the collision between the two components of ejecta, which converts the early
absorption spectrum to an emission-line spectrum within weeks of the outburst.
The narrow emission widths require the outer circumbinary gas to be much more
massive than the white dwarf ejecta, thereby slowing the latter's expansion
upon collision. The presence of a large reservoir of circumbinary gas at the
time of outburst is suggestive that novae outbursts may sometime be triggered
by collapse of gas onto the white dwarf, as occurs for dwarf novae, rather than
steady mass transfer through the inner Lagrangian point.Comment: 12 pages, 3 figures; Revised manuscript; Accepted for publication in
Astrophysics & Space Scienc
The AKARI/IRC Mid-Infrared All-Sky Survey
Context : AKARI is the first Japanese astronomical satellite dedicated to
infrar ed astronomy. One of the main purposes of AKARI is the all-sky survey
performed with six infrared bands between 9 and 200um during the period from
2006 May 6 to
2007 August 28. In this paper, we present the mid-infrared part (9um and 18um
b ands) of the survey carried out with one of the on-board instruments, the
Infrar ed Camera (IRC). Aims : We present unprecedented observational results
of the 9 and 18um AKARI al l-sky survey and detail the operation and data
processing leading to the point s ource detection and measurements. Methods :
The raw data are processed to produce small images for every scan and point
sources candidates, above the 5-sigma noise level per single scan, are der
ived. The celestial coordinates and fluxes of the events are determined
statisti cally and the reliability of their detections is secured through
multiple detect ions of the same source within milli-seconds, hours, and months
from each other. Results : The sky coverage is more than 90% for both bands. A
total of 877,091 s ources (851,189 for 9um, 195,893 for 18um) are confirmed and
included in the cur rent release of the point source catalogue. The detection
limit for point source s is 50mJy and 90mJy for the 9um and 18um bands,
respectively. The position accu racy is estimated to be better than 2".
Uncertainties in the in-flight absolute flux calibration are estimated to be 3%
for the 9um band and 4% for the 18um ban d. The coordinates and fluxes of
detected sources in this survey are also compar ed with those of the IRAS
survey and found to be statistically consistent.Comment: Accepted for publication in AandA AKARI special issu
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