4,842 research outputs found
An IUE's eye view of cool-star outer atmospheres
Three topics are discussed which together demonstrate the power of the IUE to probe the occurrences of chromospheres and coronas in the cool half of the HR diagram. These are: (1) the complementary low dispersion and echelle observing modes; (2) Mg II h and k: chromospheric cooling and width luminosity correlation; and (3) empirical correlations among chromospheric, transition region, and coronal emission. The spectra of alpha Centauri (G2 V + K1 V) and Capella (G6 III + F9 III) are compared with that of the Sun and recent low dispersion surveys of cool star emission in the 1150 A to 2000 A short wavelength region are summarized
Multi-disciplinary Investigation of the Windows of John Thornton, focusing on the Great East Window of York Minster
Twenty-seven samples of glass from panel 2e of John Thornton’s Great East Window (1405–1408) at York Minster have been analyzed using energy dispersive x-ray analysis in the scanning electron microscope. This paper highlights our findings. Inserts and replacements of early modern and medieval glass have been identifi ed. White (colorless) and colored medieval glass differ significantly in composition, suggesting diff erent sources. Eleven samples of white glass original to the window are identical within analytical error, suggesting they came from the same batch, but the head of Christ is from another panel. Blue and flashed red glass were each the product of more than one batch of melting. Primarily, the condition of the glass is dependent upon silica content. Further investigations of other panels from the Great East Window, and of other windows by Thornton, are ongoing
Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and their Isotopes
A solar photospheric "thermal profiling" analysis is presented, exploiting
the infrared rovibrational bands of carbon monoxide (CO) as observed with the
McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above
the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum
intensities and center-limb behavior constrained the temperature profile of the
deep photosphere, while CO center-limb behavior defined the thermal structure
at higher altitudes. The oxygen abundance was self consistently determined from
weak CO absorptions. Our analysis was meant to complement recent studies based
on 3-D convection models which, among other things, have revised the historical
solar oxygen (and carbon) abundance downward by a factor of nearly two;
although in fact our conclusions do not support such a revision. Based on
various considerations, an oxygen abundance of 700+/-100 ppm (parts per million
relative to hydrogen) is recommended; the large uncertainty reflects the model
sensitivity of CO. New solar isotopic ratios also are reported for 13C, 17O,
and 18O.Comment: 90 pages, 19 figures (some with parts "a", "b", etc.); to be
published in the Astrophysical Journal Supplement
Recent atmospheric neutrino results from Soudan 2
An updated measurement of the atmospheric nu_mu/nu_e ratio-of-ratios,
0.68+-0.11+-0.06, has been obtained using a 4.6-kty exposure of the Soudan-2
iron tracking calorimeter. The L/E distributions have been analyzed for effects
of nu_mu -> nu_x oscillations, and an allowed region in the Delta m^2 vs. sin^2
2 theta plane has been determined.Comment: 3 pages, 4 figures; presented at TAUP99, the 6th Int. Workshop on
Topics in Astroparticle and Underground Physics, Sept. 6-10, 1999, College de
France, Paris, Franc
The Mg 2 h and k lines in a sample of dMe and dM stars
Both Mg II h and k line fluxes are presented for a sample of 4 dMe and 3 dM stars obtained with the IUE satellite in the long wavelength, low dispersion mode. The observed fluxes are converted to stellar surface flux units and the importance of chromospheric non radiative heating in this sample of M dwarf stars is intercompared. In addition, the net chromospheric radiative losses due to the Ca II H and K lines in those stars in the sample for which calibrated Ca II H and K line data exist are compared. Active region filling factors which likely give rise to the observed optical and ultraviolet chromospheric emission are estimated. The implications of the results for homogeneous, single component stellar model chromospheres analyses are discussed
First high-resolution look at the quiet Sun with ALMA at 3 mm
We present an overview of high resolution quiet Sun observations, from disk
center to the limb, obtained with the Atacama Large mm and sub-mm Array (ALMA)
at 3 mm. Seven quiet Sun regions were observed with resolution of up to 2.5" by
4.5". We produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full disk solar
images. The images show well the chromospheric network, which, based on the
unique segregation method we used, is brighter than the average over the fields
of view of the observed regions by K while the intranetwork is less
bright by K, with a slight decrease of the network/intranetwork
contrast toward the limb. At 3 mm the network is very similar to the 1600 \AA\
images, with somewhat larger size. We detected for the first time spicular
structures, rising up to 15" above the limb with a width down to the image
resolution and brightness temperature of 1800 K above the local
background. No trace of spicules, either in emission or absorption, was found
on the disk. Our results highlight ALMA's potential for the study of the quiet
chromosphere.Comment: Astronomy and Astrophysics (Letters), in pres
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