相关论文: The coronal Ne/O abundance of alpha Centauri

We present first results from five XMM-Newton observations of the binary system Alpha Centauri, which has been observed in snapshot like exposures of roughly two hours each during the last two years. In all our observations the X-ray…

The Mg/Ne abundance ratio in the quiet Sun is measured in both network and supergranule cell centre regions through EUV spectra from the Coronal Diagnostic Spectrometer on SOHO. Twenty four sets of data over the period 1996 March to 1998…

At altitudes of about 1.05 solar radii or more, the corona above quiet solar regions becomes essentially isothermal. This obviates many of the difficulties associated with the inverse problem of determining emission measure distributions,…

Recent three-dimensional, NLTE analyses of the solar spectrum have shown a significant reduction in the C, N, O and Ne abundances leading to a Z/X ratio of the order of 0.0177. We have computed solar models with this new mixture in the OPAL…

Sensitive measurements of the interstellar gas-phase oxygen abundance have revealed a slight oxygen deficiency ($\sim$ 15%) toward stars within 500 pc of the Sun as compared to more distant sightlines. Recent $FUSE$ observations of the…

Recent studies of spectral lines of the CNO elements in the Sun and unevolved disk and halo stars show that most published abundance data may be affected by systematic errors due to inadequate 1D modelling of stellar atmospheres. This…

Determining the He/H ratio in cool stars presents a fundamental astrophysical challenge. While this ratio is established for hot O and B stars, its extrapolation to cool stars remains uncertain due to the absence of helium lines in their…

We present a measurement of the abundance of Fe relative to H in the solar corona using a technique which differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the CDS spectrometer on SOHO…

We report on the coronal activity cycles of our stellar neighbors alpha Centauri A/B. The binary has been monitored with XMM-Newton since 2002 to study the long-term evolution of coronal activity evolution in X-rays. The solar analog alpha…

The chemical composition of the Sun is a fundamental yardstick in astronomy, relative to which essentially all cosmic objects are referenced. We reassess the solar abundances of all 83 long-lived elements, using highly realistic solar…

Here we present results from over 500 kiloseconds Chandra and XMM-Newton observations of the cool core of the Centaurus cluster. We investigate the spatial distributions of the O, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni abundances in the…

Using the XMM-Newton X-ray observatory to monitor the nearest star to the Sun, Proxima Centauri, we recorded the weakest X-ray flares on a magnetically active star ever observed. Correlated X-ray and optical variability provide strong…

An extremely high-resolution (> 10^5) high-S/N (> 10^3) solar spectrum has been used to measure 15 very weak first overtone (Delta v = 2) infrared OH lines, resulting in a low solar abundance of A(O) ~ 8.6 when MARCS, 3D, and spatially and…

We present extensive new spectroscopy and imaging of PN G 135.9+55.9. We use these data as constraints to photoionization models to derive limits on the oxygen abundance. We find that PN G 135.9+55.9 has an oxygen abundance less than 1/50…

Elemental abundances in the solar corona are known to be different from those observed in the solar photosphere. The ratio of coronal to photospheric abundance shows a dependence on the first ionisation potential (FIP) of the element. We…

We show that standard solar models are in good agreement with the helioseismologically determined sound speed and density as a function of solar radius, the depth of the convective zone, and the surface helium abundance, as long as those…

The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hours exposure. We detect 1075 X-ray sources: 91% are spatially associated with…

Monte Carlo calculations of the O Kalpha line fluoresced by coronal X-rays and emitted just above the temperature minimum region of the solar atmosphere have been employed to investigate the use of this feature as an abundance diagnostic.…

Following the Chandra Orion Ultradeep Project (COUP) observation, we have studied the chemical composition of the hot plasma in a sample of 146 X-ray bright pre-main sequence stars in the Orion Nebula Cluster. We report measurements of…

The damped Lyman alpha systems seen in the spectra of high redshift QSOs offer the means to determine element abundances in galaxies observed while still at an early stage of evolution. Such measurements, which have only recently come…