Nahide G. Craig

High-resolution Ca II observations of the local interstellar medium

High-resolution absorption measurements of the interstellar Ca II K line observed toward 46 early-type stars in the local ISM (LISM) are presented. Ca II was detected in 36 of the 46 stars with 82 individual cloud components identified. Ca II was detected to most of the stars closer than 50 pc, except in the region of the Galactic quadrant l = 180-270 degrees which also contains the empty line of sight to B CMa at 220 pc. The mean local standard of rest velocity of the 82 Ca II components implies that the LISM clouds are associated with the motion of the solar neighborhood and not the sun. If the present data are combined with other nearby Ca II component velocities taken from the literature, then a cloud centered approximately at l = 90 deg, b = -40 deg moving coherently with the local interstellar wind vector is supported at a significance level of 99 percent. The Ca II data have been combined with Na I data for the same stars to produce a N(Na I)/N(Ca II) ratio for each identified absorption feature. This ratio plotted against the local standard of rest velocities of the clouds shows that the Routly-Spitzer effect exists down to +/- 10 km/s, which supports grain desorption/destruction models that are efficient at returning calcium to the gas phase at these low velocities.

The local distribution of Na I interstellar gas

We present high-resolution absorption measurements (lambda/Delta lambda approximately 75,000) of the interstellar Na I D lines at 5890 A toward 80 southern hemisphere early-type stars located in the local interstellar medium (LISM). Combining these results with other sodium measurements taken from the literature, we produce galactic maps of the distribution of neutral sodium column density for a total of 293 stars generally lying within approximately 250 pc of the Sun. These maps reveal the approximate shape of the mid-plane contours of the rarefied region of interstellar space termed the Local Bubble. Its shape is seen as highly asymmetric, with a radius ranging from 30 to 300 pc, and with an average radius of 60 pc. Similar plots of the Galactic mid-plane distribution of sources emitting extreme ultraviolet radiation show that they also trace out similar contours of the Local Bubble derived from Na I absorption measurements. We conclude that the Local Bubble absorption interface can be represented by a hydrogen column density, Nu(sub ETA) = 2 x 10(exp 19) cm(exp -2), which explains both the local distribution of Na I absorption and the observed galactic distribution of extreme ultraviolet sources. The derived mid-plane contours of the Bubble generally reproduce the large-scale features carved out in the interstellar medium by several nearby galactic shell structures.

The Extreme Ultraviolet Explorer Stellar Spectral Atlas

We present an atlas of extreme ultraviolet (EUV) spectra of 95 bright stellar sources observed between 1992 July and 1996 June with the Extreme Ultraviolet Explorer (EUVE) spectrometers. These data are taken in the short- (SW; 70-190 A), medium- (MW; 140-380 A), and long-wavelength bandpasses (LW; 280-760 A) at roughly 0.5, 1, and 2 A resolution, respectively. We describe the spectrometers and detail the procedure used to reduce the observational data to spectra. The atlas is grouped by the type of source: O-A stars, F-M stars, white dwarfs, and cataclysmic variables. We present a brief overview of the general nature and EUV spectral distribution of each group and present accompanying notes and individual spectra for each source. We show selected F-M sources in more detail with identifications of the brightest spectral lines illustrating the characteristics of the EUV spectra of stars of various temperatures. The current study is the most complete compilation to date of aggregate spectra of bright EUV stellar sources.

A Minisurvey of Interstellar Titanium from the Southern Hemisphere

We describe the results of a minisurvey of interstellar Ti II and Ca II absorption toward 42 early-type stars observed from the southern hemisphere at a spectral resolution of 4.5 km s-1. Results are also presented for the Na I ultraviolet line (3302 A) detected toward nine of these targets. We examine the dependence of the integrated column densities of N(Ti II), N(Ca II), and N(Na I) on distance, reddening, neutral hydrogen column density, and their Galactic elemental abundance. Our findings support the proposition that Ti II and Ca II absorption originates in the same regions of the pervasive, warm, and neutral intercloud gas of the interstellar medium. We have observed a correlation of decreasing Ti and Ca abundance with increasing line-of-sight gas density. The Ti II/Ca II abundance ratio has been found to be essentially constant under all the interstellar density conditions we have sampled. Thus, we conclude that the general absorption properties of titanium (and calcium) are similar throughout the entire disk of our Galaxy.

Serendipitous EUV sources detected during the first year of the Extreme Ultraviolet Explorer right angle program

We report the detection of 114 extreme ultraviolet (EUV; 58 - 740 A) sources, of which 99 are new serendipitous sources, based on observations made with the imaging telescopes on board the Extreme Ultraviolet Explorer (EUVE) during the Right Angle Program (RAP). These data were obtained using the survey scanners and the Deep Survey instrument during the first year of the spectroscopic guest observer phase of the mission, from January 1993 to January 1994. The data set consists of 162 discrete pointings whose exposure times are typically two orders of magnitude longer than the average exposure times during the EUVE all-sky survey. Based on these results, we can expect that EUVE will serendipitously detect approximately 100 new EUV sources per year, or about one new EUV source per 10 sq deg, during the guest observer phase of the EUVE mission. New EUVE sources of note include one B star and three extragalactic objects. The B star (HR 2875, EUVE J0729 - 38.7) is detected in both the Lexan/B (approximately 100 A) and Al/Ti/C (approximately 200 A) bandpasses, and the detection is shown not to be a result of UV leaks. We suggest that we are detecting EUV and/or soft x rays from a companion to the B star. Three sources, EUVE J2132+10.1, EUVE J2343-14.9, and EUVE J2359-30.6 are identified as the active galactic nuclei MKN 1513, MS2340.9-1511, and 1H2354-315, respectively.

Further high-resolution Na I observations of the local interstellar medium

High-resolution absorption measurements of the interstellar Na I D lines at 5890 A observed toward 27 early-type stars in the local interstellar medium (LISM) are presented. These results are combined with other high-resolution sodium measurements to map the space distribution of neutral sodium column density for some 118 stars out to less than 200 pc. These measurements indicate an upper limit to the neutral sodium column density of log N(Na I) less than 10.0/sq cm can be inferred out to a distance of 50 pc in most directions in the LISM. Also, the rarefield region of the Local Bubble may extend beyond 60 pc in at least 35 percent of the directions sampled thus far. Evidence is shown for a ubiquitous, comoving vector for neutral NaI gas clouds in the LISM which is in a different direction to LISM vectors previously reported for more ionized local gas clouds. A comparison of the measured sodium columns with those of interstellar Ca II for a sample of 12 stars within 95 pc results in a ratio of Na I/Ca II less than 0.5 for most stars. This value implies that there could be warm, neutral gas with T of about 12,500 K beyond 50 pc in the LISM.

Determination of (C-12)/(C-13) in the interstellar medium toward Zeta Ophiuchi and Xi Persei

The Lick Observatory Reticon (LOR) data presented in Hawkins et al. (1985) are reanalyzed in order to determine the cause of the significant discrepancy in (C-12)/(C-13) isotope ratios determined on the basis of observations of this isotope in the interstellar medium toward Zeta Ophiuchi and Xi Persei. A new set of Lick Observatory observations toward Zeta Oph are obtained using a CCD detector. The KPNO coude feed echelle spectrograph and a CCD detector are used to carry out high-resolution, high SNR ratio observations toward Zeta Oph and Xi Per. The LOR results for Zeta Oph are uncertain, ranging to 40 to 60, owing to the error in continuum placement. The KPNO results toward Zeta Oph are (C-12)H/(C-13)H(+)(0, 0) = 63 +/- 8, (C-12)H(+)/(C-13)H(+)(1, 0) = 67 +/- 19, and (C-12)N/(C-13)N = 100 + 88/- 33. Toward Xi Per, the KPNO measurements yield (C-12)H(+)/(C-13)H(+) = 49 +/- 15 from the 4232-A band, and a lower limit of 45 from the 3957-A observations.

Spectroscopy and Photometry of EUVE J1429-38.0:An Eclipsing Magnetic Cataclysmic Variable

EUVE J1429-38.0 was originally discovered as a variable source by the Extreme Ultraviolet Explorer {EUVE) satellite. We present new optical observations which unambiguously confirm this star to be an eclipsing magnetic system with an orbital period of 446. The photometric data are strongly modulated by ellipsoidal variations during low states which allow a system inclination of near 80 degrees to be determined. Our time-resolved optical spectra, which cover only about one-third of the orbital cycle, indicate the clear presence of a gas stream. During high states, EUVE J1429-38.0 shows ~ 1 mag deep eclipses and the apparent formation of a partial accretion disk. EUVE J1429-38.0 presents the observer with properties of both the AM Herculis and the DQ Herculis types of magnetic cataclysmic variable.

Extreme Ultraviolet Explorer Optical Identification Campaign. IV. A Northern Hemisphere Sample of Active Late-Type Stars and Typical EUV Sources

We present new optical identifications of previously unidentified faint extreme ultraviolet sources. Our total sample of 30 identified sources, of which 22 are new identifications, includes 24 late-type stars, three white dwarfs, two cataclysmic variables (CVs), and one active galactic nucleus. These sources are joint detections of the faint sources from the all-sky surveys of the Extreme Ultraviolet Explorer (EUVE) in the 58–174 A (0.071–0.214 keV) EUV band and of the ROSAT Position Sensitive Proportional Counter in the 5–120 A (0.1–2.4 keV) X-ray band. We obtained medium-resolution spectra of the possible optical counterparts with the Shane 3 m telescope at Lick Observatory using the Kast double spectrograph covering a bandpass of 3600–7500 A. Our sample of active late-type stars is dominated by K and M stars showing strong Balmer and Ca II emission lines. The white dwarfs are fairly typical for those detected in the EUVE survey with Teff and log g ranging from 35 to 53 kK and 7.6 to 8.7, respectively. We found strong H and He emission lines typical of cataclysmic variables (CVs) for EUVE J0854+390 and EUVE J1802+180. EUVE J0854+390 is a newly identified cataclysmic variable showing radial velocity shifts to the red as large as ≈400 km s-1. We associate EUVE J1802+180 with the previously identified CV, V884 Her (RX J1802.1+1804). Including the present work (22 new identifications), EUVE optical identification campaigns have identified ≈28% of the presently cataloged NOID sources.

EUVE J1429–38.0: A New Magnetic Cataclysmic Variable

The source EUVE J1429-38.0 was discovered serendipitously by the Extreme Ultraviolet Explorer (EUVE) satellite on 1993 March 5. Optical spectroscopy confirms a cataclysmic variable-type optical counterpart for the source, showing Balmer, He I, and Ca emission, as well as strong He II emission. The optical spectrum, the apparent high/low state behavior, and possible weak cyclotron humps visible in the spectrum indicate that this star is likely to be an AM Herculis system, but the possibility of being a DQ Her, or an unlocked AM Her system, cannot be excluded. Analysis of the highly modulated EUVE photometry yields a period of 2 hr 22 minutes, which we conclude is the binary orbital period. In addition, a 57 minute period is also present. An orbital period of 2.5 hr would make EUVE J1429-38.0 only the third known AM Her system within the cataclysmic variable period gap, all three of which were discovered through EUV observations.