1,823 research outputs found
Large area low-cost space solar cell development
A development program to produce large-area (5.9 x 5.9 cm) space quality silicon solar cells with a cost goal of 30 $/watt is descibed. Five cell types under investigation include wraparound dielectric, mechanical wraparound and conventional contact configurations with combinations of 2 or 10 ohm-cm resistivity, back surface reflectors and/or fields, and diffused or ion implanted junctions. A single step process to cut cell and cover-glass simultaneously is being developed. A description of cell developments by Applied Solar Energy Corp., Spectrolab and Spire is included. Results are given for cell and array tests, performed by Lockheed, TRW and NASA. Future large solar arrays that might use cells of this type are discussed
Solar cell development for the power extension package
The PEP is a 32 kilowatt flexible substrate, retrievable, solar array system for use on the Space Shuttle. Solar cell costs will be reduced by increasing cell area and simplifying cell and coverglass fabrication processes and specifications. The cost goal is to produce cells below $30 per watt. Two and ten ohm-cm silicon cells were investigated. In phase I of the cell development program a few thousand candidate cells will be produced and evaluated for utility and quality. In phase II a large number of cells will be fabricated to verify production readiness and cell yields and costs. This schedule is compatible with PEP initial operational capability in 1984. Approximately 140,000 large area (5.9 x 5.9 cm) cells will be required for two PEP solar arrays. The status of the cell development and testing, including a radiation damage test and side-by-side comparison of candidate cell types with pre- and post-irradiation airplane calibration of outer space short-circuit current, is reported
On the usefulness of finding charts Or the runaway carbon stars of the Blanco & McCarthy field 37
We have been recently faced with the problem of cross--identifying stars
recorded in historical catalogues with those extracted from recent fully
digitized surveys (such as DENIS and 2MASS). Positions mentioned in the old
catalogues are frequently of poor precision, but are generally accompanied by
finding charts where the interesting objects are flagged. Those finding charts
are sometimes our only link with the accumulated knowledge of past literature.
While checking the identification of some of these objects in several
catalogues, we had the surprise to discover a number of discrepancies in recent
works.The main reason for these discrepancies was generally the blind
application of the smallest difference in position as the criterion to identify
sources from one historical catalogue to those in more recent surveys. In this
paper we give examples of such misidentifications, and show how we were able to
find and correct them.We present modern procedures to discover and solve
cross--identification problems, such as loading digitized images of the sky
through the Aladin service at CDS, and overlaying entries from historical
catalogues and modern surveys. We conclude that the use of good finding charts
still remains the ultimate (though time--consuming) tool to ascertain
cross--identifications in difficult cases.Comment: 4 pages, 1 figure, accepted by A&
The AGB population of NGC 6822: distribution and the C/M ratio from JHK photometry
NGC 6822 is an irregular dwarf galaxy and part of the Local Group. Its close
proximity and apparent isolation provide a unique opportunity to study galactic
evolution without any obvious strong external influences. This paper aims to
study the spatial distribution of the asymptotic giant branch (AGB) population
and metallicity in NGC 6822. Using deep, high quality JHK photometry, taken
with WFCAM on UKIRT, carbon- and oxygen-rich AGB stars have been isolated. The
ratio between their number, the C/M ratio, has then been used to derive the
[Fe/H] abundance across the galaxy. The tip of the red giant branch is located
at K0 = 17.41 \pm 0.11 mag and the colour separation between carbon- and
oxygen-rich AGB stars is at (J - K)0 = 1.20 \pm 0.03 mag (i.e. (J - K)2MAS S
{\guillemotright} 1.28 mag). A C/M ratio of 0.62 \pm 0.03 has been derived in
the inner 4 kpc of the galaxy, which translates into an iron abundance of
[Fe/H] = -1.29\pm0.07 dex. Variations of these parameters were investigated as
a function of distance from the galaxy centre and azimuthal angle. The AGB
population of NGC 6822 has been detected out to a radius of 4 kpc giving a
diameter of 56 arcmin. It is metal-poor, but there is no obvious gradient in
metallicity with either radial distance from the centre or azimuthal angle. The
detected spread in the TRGB magnitude is consistent with that of a galaxy
surrounded by a halo of old stars. The C/M ratio has the potential to be a very
useful tool for the determination of metallicity in resolved galaxies but a
better calibration of the C/M vs. [Fe/H] relation and a better understanding of
the sensitivities of the C/M ratio to stellar selection criteria is first
required
The metallicity gradient as a tracer of history and structure : the Magellanic Clouds and M33 galaxies
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO) DOI: 10.1051/0004-6361/200912138Context. The stellar metallicity and its gradient place constraints on the formation and evolution of galaxies. Aims. This is a study of the metallicity gradient of the LMC, SMC and M33 galaxies derived from their asymptotic giant branch (AGB) stars. Methods. The [Fe/H] abundance was derived from the ratio between C- and M-type AGB stars and its variation analysed as a function of galactocentric distance. Galaxy structure parameters were adopted from the literature. Results. The metallicity of the LMC decreases linearly as â0.047±0.003 dex kpcâ1 out to âŒ8 kpc from the centre. In the SMC, [Fe/H] has a constant value of âŒâ1.25 ± 0.01 dex up to âŒ12 kpc. The gradient of the M33 disc, until âŒ9 kpc, is â0.078 ± 0.003 dex kpcâ1 while the outer disc/halo, out to âŒ25 kpc, has [Fe/H] ⌠â1.7 dex. Conclusions. The metallicity of the LMC, as traced by different populations, bears the signature of two major star forming episodes: the first one constituting a thick disc/halo population and the second one a thin disc and bar due to a close encounter with the Milky Way and SMC. The [Fe/H] of the recent episode supports an LMC origin for the Stream. The metallicity of the SMC supports star formation, âŒ3 Gyr ago, as triggered by LMC interaction and sustained by the bar in the outer region of the galaxy. The SMC [Fe/H] agrees with the present-day abundance in the Bridge and shows no significant gradient. The metallicity of M33 supports an âinsideoutâ disc formation via accretion of metal poor gas from the interstellar medium.Peer reviewe
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