Chandra, EUVE, HST, and VLA multiwavelength campaign on HR 1099: Instrumental capabilities, data reduction, and initial results

In mid-September of 1999, a multiwavelength campaign was carried out on the coronally active RS Canum Venaticorum binary HR 1099 (K1 IV + G5 V; P = 2. 84 days), during commissioning of the High Energy Transmission Grating Spec trometer (HETGS) of the Chandra X-ray Observatory (CXO). The coordinated pr ogram involved the Extreme Ultraviolet Explorer (EUVE), the Hubble Space Te lescope Imaging Spectrograph (STIS), and the Very Large Array (VLA). The ob jective was to study the system in quiescence, across as much of the electr omagnetic spectrum as practical, and to catch any flares that might occur. The EUVE 80-180 Angstrom light curve of HR 1099, covering the period Septem ber 13-22, showed only a single impulsive outburst, which occurred at the v ery end of the 9 day pointing. The 3-25 Angstrom bremsstrahlung continuum d isplayed an overall decay during the 1.5 day Chandra observation on Septemb er 14-16, with a few superimposed mild enhancements. The VLA 3.5 cm and 20 cm radio light curves, obtained during a 10 hr period on September 15 immed iately before the HST pointing, similarly revealed normal quiescent gyrosyn chrotron emission and an absence of impulsive events. In contrast, the 7 hr STIS time series later on September 15 contained two distinct flares. The first was accompanied by intensification of the preexisting broad wings of the medium excitation species (e.g., Si IV lambda 1393 and C IV lambda 1548 ), while the second involved primarily the narrow cores of the lines, and e ven cooler temperatures. The Fe XXI lambda 1354 forbidden line showed littl e response to either flare, consistent with the contemporaneous soft X-ray and EUV light curves. The lack of coronal counterparts to the ultraviolet f lares is unusual and suggests that they belong to a separate class of outbu rsts, sharing some similarities with the "transition zone explosive events" seen on the Sun. The density sensitive O IV lambda 1400 multiplet was not affected by either flare. The density sensitive Si III lambda 1300 multiplet showed little re sponse to the first flare, but a dramatic brightening in the second, likely due to the lower peak temperature of that event. The O IV line ratios were near their low-density limits and suggest n(e) similar to 10(10) cm(-3) fo r the duration of the HST observations. The Si III ratios during the second flare rise indicate n(e) similar to 7 x 10(10) cm(-3). The far-UV diagnost ics jointly imply electron pressures of n(e) T similar to 2 x 10(15) K cm(- 3), if formed close to their respective ionization equilibrium temperatures . The helium-like triplets of O VII, NeIX, and Mg XI in the HETGS spectra h ave forbidden-tointercombination line ratios consistent with average corona l electron densities of less than or similar to 10(11) cm(-3) at T similar to 0.3-1 x 10(7) K over the duration of the Chandra pointing. Fe XXI lambda 102/lambda 128 and lambda 142/lambda 128 ratios from EUVE suggest n(e) les s than or similar to 10(12)-10(13) cm(-3), near 10(7) K. Thus, the coronal electron pressures could be as much as several orders of magnitude larger t han those of the lower atmosphere. We constructed time-resolved spectra from the HETGS event lists and measure d the centroids of the three brightest X-ray lines of HR 1099 in 60 minute bins. In high-S/N Ne x lambda 12.1, we believe that we can see the changing radial velocity of the K1 IV star over the half an orbital cycle recorded by Chandra. The amplitude of the velocity change is only similar to 100 km s(-1) over the 1.5 day interval, a small fraction of the 300-500 km s(-1) r esolution of the HETGS at 12 Angstrom. Ne x lambda 12.1 also displayed a tr ansient blueshift of similar to 60 km s(-1) immediately prior to the first STIS flare, during which the far-UV lines briefly exhibited blueshifts of s imilar magnitude. The apparent displacement of Ne x appears independently i n the -1 and +1 orders of the medium energy band (MEG), but there was no co nfirmation in the redundant high energy band (HEG), nor in other X-ray line s. Fe XXI lambda 1354 showed a blueshift about 30 minutes later at the begi nning of the second HST orbit, but only at the 20 km s(-1) level. Analogous HETGS time series of the brightest lines of comparison star Capella (alpha Aurigae; G8 III + G1 III) exhibited steady behavior, consistent with measu rement uncertainties, without the transient Doppler "bursts" seen in HR 109 9. Although the reality of the Ne x Ly alpha blueshift is in doubt, there i s no question that the Chandra HETGS velocity scales are stable and free fr om large systematic errors.