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Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
The Infrared Array Camera (IRAC) on the Spitzer Space Telescope isabsolutely calibrated by comparing photometry of a set of A stars nearthe north ecliptic pole to predictions based on ground-basedobservations and a stellar atmosphere model. The brightness of pointsources is calibrated to an accuracy of 3%, relative to models forA-star stellar atmospheres, for observations performed and analyzed inthe same manner as for the calibration stars. This includes correctionsfor the location of the star in the array and the location of thecentroid within the peak pixel. Long-term stability of the IRACphotometry was measured by monitoring the brightness of A dwarfs and Kgiants (near the north ecliptic pole) observed several times per month;the photometry is stable to 1.5% (rms) over a year.Intermediate-timescale stability of the IRAC photometry was measured bymonitoring at least one secondary calibrator (near the ecliptic plane)every 12 hr while IRAC was in nominal operations; the intermediate-termphotometry is stable, with a 1% dispersion (rms). One of the secondarycalibrators was found to have significantly time-variable (5%)mid-infrared emission, with a period (7.4 days) matching the opticallight curve; it is possibly a Cepheid variable.
| RE 0044+09: A new K dwarf rapid rotator with a white dwarf companion
We report the discovery of a new K dwarf rapid rotator with a potentialwhite dwarf companion. The white dwarf accounts for over 90% of theobserved extreme ultraviolet flux detected from this system. Analysis ofROSAT Wide Field Camera (WFC) and IUE data both suggest a white dwarftemperature of approximately 28,700 K. Optical photometry and the IUElong wavelength prime (LWP) spectrum (with the white dwarf contributionremoved) imply that the late-type star has a spectral type of K1-3 V,and a distance of 55 +/- 5 pc. Using this distance, the observed IUE SWPflux, and the best-fit temperature results in a white dwarf radius of0.0088 solar radius. The estimated white dwarf mass is thenapproximately 0.91 solar mass; somewhat over-massive compared to fieldwhite dwarfs. Optical photometry of the K star reveals a 'spot'modulation period of approximately 10 hr (now observed over 3 yr).However, radial velocity observations have revealed no significantvariations. Spectroscopic observations place a low limit on the lithiumabundance, but do show rapid rotation with a v sin i of 90 +/- 10 km/s.The K star was detected as a radio source at 3.6 cm (on two occasions)and 6 cm by the Very Large Array (VLA). The most likely evolutionaryscenario is that the K star and hot white dwarf from either a widebinary or common proper motion pair with an age of 0.1-0.1Gyr-consistent with the evolutionary timescale of the white dwarf andthe rapid rotation of the K star. However, from the proper motion of theK star, this system does not seem to be associated with any of the knownyoung stellar groups.
| Photoelectric measurements of lunar occultation. VI. Further observational results.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973AJ.....78..482D&db_key=AST
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