Zeta Oph Research Articles

Time-Series Observations of O Stars. II. Optical Observations of zeta Ophiuchi

We present photopolarimetry and extensive high-resolution, high-signal-to-noise optical spectroscopy of the rapidly rotating late O-type star zeta Ophiuchi (HD 149757). The polarimetric data show no substantial variability over 1 week (sigma(p) < 0.04%), while the spectroscopic data show characteristic line-profile variations in the form of ''bumps'' migrating from blue to red on typical time scales of several hours. These variations are relatively strong (amplitude approximately 1% of the continuum level) in He I lambda4471, and Si III lambdalambda4552, 4567, 4575. They are seen at lower amplitudes in Mg II lambda4481, but are almost undetectable (amplitude less than or similar to 0.3%) in He II lambdalambda4541, 4686 and N III lambdalambda4511, 4515, 4518. We attribute this to a combination of equatorial gravity darkening and a latitudinally confined origin of the variations.Using a Fourier CLEAN technique, it is shown that the line-profile variations can be adequately represented as a set of sinusoids. The periods, combined with an estimate of the rotational period, lead us to rule out rotational modulation as the origin of the variability. The phase changes of the sinusoids across the line-profiles indicate a repetitive pattern, consistent with sectorial (l = -m) nonradial pulsation. We find four periods: P = 3.339 hr (Absolute value of m = 4), 2.435 hr (Absolute value of m = 5 or 6), 1.859 hr (Absolute value of m = 9 +/- 1), and either 1.366 or 1.292 hr (Absolute value of m = 11 +/- 1). The ''superperiods,'' P Absolute value of m, may be nearly commensurate (at approximately 13-14 hr), but that commensurability is not exact.

Time-Series Observations of O Stars. III. IUE and HST Spectroscopy of zeta Ophiuchi and Implications for the ``Photospheric Connection''

Stellar-wind variability in the archetypal nonradially pulsating O star ζ Oph (O9.5 V) is discussed on the basis of new time-series IUE and HST spectroscopy and archival results. Time-variable discrete absorption components are first observed at high velocities (≥10 3 km s −1 ≃0.8v∞) and then migrate blueward; the recurrence time scale for the phenomenon is ∼20 hr. This is the first record of this type of variability in a luminosity-class V star and provides support for the previously inferred ubiquity of such behavior across the O-star regime. The accelerations are slower than predicted by steady state wind models and are unlikely to represent the time-averaged velocity law of the outflow

Density, temperature, and isotopic abundance in molecular gas around Zeta Ophiuchi

view Abstract Citations (8) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Density, Temperature, and Isotopic Abundance in Molecular Gas around zeta Ophiuchi Liszt, Harvey S. Abstract The J = 2-1 lines of (C-12)O and (C-13)O have been observed around Zeta Oph at positions corresponding to the earlier J = 1-0 data of Liszt (1992), in order to determine the number density, temperature, and isotopic abundance ratio. The observations are consistent with a range of physical conditions. For temperatures of 20-40 K, the H2 number density is only 50 percent higher at the J = 1-0 emission peak than toward the star, the column density is larger by a factor of a few, and the (C-12)O/(C-13)O column density ratio is 60. For Tk not greater than 10 K, both the CO column density and H2 number density would be larger by factors of 5-20 (compared to the line of sight toward Zeta Oph), and the isotope ratio in CO would be greater than 89. Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/173072 Bibcode: 1993ApJ...414..242L Keywords: Carbon Monoxide; Carbon 13; Gas Density; Gas Temperature; Molecular Gases; Ophiuchi Clouds; Abundance; Interstellar Gas; Interstellar Matter; Line Of Sight; Astrophysics; ISM: ABUNDANCES; ISM: MOLECULES; STARS: INDIVIDUAL CONSTELLATION NAME: ZETA OPHIUCHI full text sources ADS | data products SIMBAD (1) Related Materials (1) Erratum: 1994ApJ...424..510L

Detection of boron, cobalt, and other weak interstellar lines toward Zeta Ophiuchi

Numerous weak lines from interstellar atomic species toward Zeta Ophiuchi were observed with the Goddard High-Resolution Spectrograph. Of particular note are the first interstellar detection of cobalt and the detection of boron in this sight line. These measurements provide estimates for the amount of depletion for the two elements. Boron, a volatile, and cobalt, a refractory element, display the depletion pattern found by Savage et al. (1992). The abundance of phosphorus in the H II region associated with the star was obtained from a detection of P III. Additional weak lines from S I, C I, Ni II, and Cu II were detected for the first time; these lines provide the basis for refinements in oscillator strength and column density. Analysis of the neutral sulfur data indicates that the atomic gas is more widely distributed than the molecular material in the main component.

The interstellar Li-7/Li-6 isotope ratio toward Zeta Ophiuchi and Zeta Persei

High S/N, high-resolution observations of the interstellar Li absorption lines toward the stars Zeta Ophiuchi and Zeta Persei are reported. Li I line profiles indicate the presence of both the Li-7 and Li-6 doublets in these two sightlines. Best-fit values for the interstellar Li-7/Li-6 isotope ratio are 6.8 (+1.4/-1.7) towards Zeta Ophiuchi and 5.5 (+ 1.3/-1.1) toward Zeta Persei. Measurement of 6.8 (+1.4/-1.7) for the interstellar Li-7/Li-6 isotope ratio towards Zeta Ophiuchi does not support the lower limit of 25 determined by Ferlet and Dennefeld (1984). The current value of the interstellar Li-7/Li-6 isotope ratio is the result of various lithium production and destruction processes involving stars, cosmic rays, and the big bang.

CH as a tracer of a translucent cloud boundary

view Abstract Citations (20) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CH as a Tracer of a Translucent Cloud Boundary Magnani, Loris ; Onello, Joseph S. Abstract We report the detection of broad wings in the CH 3335 MHz hyperfine ground state transition for three positions in the high-latitude molecular cloud MBM 16. These wings are not due to star formation and are not detected with the CO(J = 1-0) line. They may be the radio analog of broad CH lines recently noted in optical spectra of the diffuse cloud in front of Zeta Oph. Since the CH wings are not visible with the CO(J = 1-0) transition, they may provide a way to trace the low-density molecular hydrogen gas in the region between the dense molecular portion of the cloud and the surrounding atomic hydrogen envelope. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172613 Bibcode: 1993ApJ...408..559M Keywords: Hydrocarbons; Hyperfine Structure; Interstellar Matter; Methylidyne; Molecular Clouds; Molecular Gases; Radio Spectra; Electron Transitions; Emission Spectra; Line Of Sight; Astrophysics; ISM: CLOUDS; ISM: INDIVIDUAL ALPHANUMERIC: MBM 16; ISM: MOLECULES full text sources ADS | data products SIMBAD (1)

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.

Abundance of interstellar carbon toward Zeta Ophiuchi

We report on the detection of the weak intersystem transition of semiforbidden C II 2325 A in the sight line toward Zeta Oph using the Ech-B mode of the Goddard High-Resolution Spectrograph. The measured equivalent width of the semiforbidden C II line is W(lambda) = 0.52 +/- 0.12 mA, implying a C II column density of 1.80 (+/- 0.42) x 10 exp 17 atoms/sq cm and (C/H) sub Zeta Oph = 1.32 (+/- 0.32) x 10 exp -4.

Nonradial Oscillations in Zeta Ophiuchi in 1991

The line-profile variations have been found in many early-type stars surrounding the classical β Cephei variables in the H-R diagram. The feature of the variations has not been known enough mainly because of their periods of about one day. To specify the cause of the variations, however, it is necessary to make clear their features such as the multi-periodicity, the relation between the photometric variations and the spectroscopic ones, and the cause of existence or non-existence of mode (or period) switching (Balona 1991, Smith 1991). In Be stars, the correlation of the amplitude of the variations with their emission cycle is also important (Ando 1986).

Ultraviolet observations of the gas phase abundances in the diffuse clouds toward Zeta Ophiuchi at 3.5 kilometers per second resolution

Goddard High Resolution Spectrograph echelle mode measurements at 3.5 km/s resolution are presented for interstellar absorption produced by C II, O I, Mg I, Mg II, Al III, P II, Cr II, Mn II, Fe II, Ni II, Cu II, Zn II, Ga II, Ge II, and Kr I. The absorption line measurements are converted into representations of apparent column density per unit velocity in order to study the multicomponent nature of the absorption. The high spectral resolution of the measurements allows a comparative study of gas phase abundances for many species in the absorbing clouds near -27 and -15 km/s with a typical precision of about 0.05 dex. The matter absorbing near -27 km/s is situated in the local interstellar medium and has log N(H I) of about 19.74. This absorption provides information about the modest 'base' depletion associated with the lower density interstellar medium. The depletion results suggest that accretion processes are operating interstellar clouds that exhibit similar depletion efficiencies for some elements but much higher depletion efficiencies for others.

Interstellar absorption along the line of sight to Theta Carinae using Copernicus observations

A profile fitting technique is employed to identify the velocities and Doppler b values for H I and H II clouds along the line of sight to Theta Car. Total abundances and depletions for 12 elements, plus column densities for the J = 0 to J = 5 rotational levels of H2 are obtained. Electron densities for both clouds are calculated from the ratios of the fine-structure levels of C II and N II, obtaining 0.08/cu cm and 1.2/cu cm. The fine-structure levels of C I, which led to 120/cu cm, are used to calculate the neutral hydrogen density for the H I region. D I is also present in the data from the Theta Car line of sight, yielding a D/H ratio of 5 x 10 exp -6. Elemental depletions are calculated for the H I region as well. Comparison of the results for Theta Car and those for Zeta Oph and Alpha Vir shows that the absolute depletions are different; however, the relative depletions are remarkably stable for different physical conditions.

Fractionation of CO in the diffuse clouds toward Zeta Ophiuchi

An analysis of CO A-X bands in diffuse clouds toward Zeta Ophiuchi is presented. The results provide isotopic ratios that constitute the strongest observational evidence for highly localized isotopic fractionation of CO in diffuse portions of an interstellar cloud. The value of the fractionation implies that selective photodissociation is the controlling influence of the fractionation. The molecule's excitation temperature is discussed and a lower limit to the O-16/O-18 ratio is provided. The absence of CO lines from the gas that provides broad CH+ and CH lines commonly attributed to warm gas behind a shock front is addressed.

A SEARCH FOR WEAK ULTRAVIOLET INTERSTELLAR ABSORPTION FEATURES IN IUE SPECTRA OF RHO OPHIUCHI AND ZETA OPHIUCHI

ABSTRACT We have applied procedures designed to reduce substantially the non-random, so-called "fixed-pattern" noise present in IUE spectra to archival long-wavelength light-dispersion spectra of rho Ophiuchi and zeta Ophiuchi. Substantial elimination of the fixed-pattern noise via flat fielding can yield 2-sigma equivalent width limits of 5-10 mA from the sum of a small number (< 5) of well exposed archival spectra, and increases confidence in the reality of any weak features found. Examination of complete long-wavelength ( 2200-3250 A) spectra of these two stars has revealed, in addition to many known strong absorption lines, several lines of Fe I and Si I which had not previously been reported, as well as a small number of opssible unidentified lines. We also present substantially improved upper limits to the equivalent widths of a number of other weak lines; limits an order of mganitude smaller, now achievable with the HST GHRS, should produce detections of some of these.

The diffuse interstellar cloud toward HD 179406 (20 Aquilae)

An analysis of the diffuse interstellar cloud complex in front of HD 179406 (20 Aql) is presented. Along this sight line, multispectral absortion- and emission-line studies have uncovered at least three distinct velocity components due to individual clouds. A dominant velocity component is seen in both the absorption and emission-line data sets at 3 +/- 1 km/s. It is argued that the cloud associated with this velocity component is responsible for most of the atomic and all of the molecular gas in front of 20 Aql. The present chemical and physical analysis of the cloud combines the diagnostic tools of radio emission-line data with those of UV and optical absorption data. Using non-LTE models to synthesize the observed absorption profiles, (C-12)O and (C-13)O column densities along this line of sight are determined. The (C-12)O/(C-13)O abundance ratio was found to be 50 +/- 15, similar to that found by Wannier et al. toward Zeta Oph. The physical conditions of the cloud have been investigated using ultraviolet absorption lines. Measurements indicate that the dominant absorption cloud has a gas pressure similar to that found in the local diffuse molecular cloud in Ophiuchus with nT = 20,000/cu cm K.

Kinematics and morphology of material occulting Zeta Ophiuchi

Observations of λ2.6 mm 12 CO emission taken along a 2° strip about the position of ζ Oph show a strikingly coherent kinematic pattern. Within 30'of the star, 12 CO attains antenna temperatures of 3-5 K, more like dark than diffuse clouds. However, the 12 CO/ 13 CO intensity ratio is ≥ 31:1 even when the 12 CO line as strong as 5.5 K, which is highly unusual. It is suggested that the CO line brightness is dominated by recombination and excitation effects in gas which is strongly affected by the presence of the star

Interstellar gas phase abundance of carbon, oxygen, nitrogen, copper, gallium, germanium, and krypton toward Zeta Ophiuchi

An analysis of weak (less than 10 mA) UV interstellar absorption line data obtained for the line of sight to the O9.5 IV star Zeta Oph is presented. Measurements of weak semiforbidden lines of N I, O I, Cu II, and a new UV detection of Na I are reported along with a small upper limit for C II. Interstellar detections of Ga II, Ge II, and Kr I are also presented. Ga, Ge, and Kr represent the heaviest elements detected in the ISM. A comparison of the derived column densities to cosmic abundances shows Ga to be depleted by about -1.2 dex while Ge is overabundant by +0.2 dex. Assuming Kr to be undepleted, a logarithmic cosmic abundance of Kr/H = 2.95 is obtained on the scale where H = 12.00.

The interstellar (C-12)N/(C-13)N ratio toward Zeta Persei

High-resolution, high signal-to-noise observations of interstellar CN toward Zeta Per are performed to determine the C-12/C-13 isotope ratio in this line of sight. Observations of (C-12)N/(C-13)N in several diffuse clouds are performed to assess whether CN suffers from isotope-selective effects. Values are obtained which are higher than the value toward Zeta Oph determined by Crane and Hegyi (1988) and lower than the results toward the more reddened stars HD 21483 obtained by Meyer et al. (1989) and Palazzi et al. (1990). Theory and observations indicate the existence of a spatial C-12/C-13 gradient which decreases toward the Galactic center at an approximate rate of 12 percent/kpc at the distance of the solar radius. It is argued that since a gradient of this character cannot explain the CN results, isotope-selective effects provide a more likely explanation for the large range in (C-12)N/(C-13)N ratios.

Probing shock models of CH(+) formation

view Abstract Citations (17) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Probing Shock Models of CH + Formation Hawkins, Isabel ; Craig, Nahide Abstract High-resolution, high SNR observations of CH and CH(+) toward Zeta Oph, Xi Per, and P Cyg are used to test several predictions of shock models of molecule formation. The predicted differences between the CH and HCH(+) heliocentric velocities of the magnitude produced by the shock theories are not found in any of the three stars. toward Zeta Oph and Xi Per, no difference is found, based on high-quality data, between the observed CH(+) lie profiles and a Gaussian function which would be expected as a result of shock structure. Gaussian line width parameters of CH(+) lines toward Zeta Oph and Xi Per are broad as predicted by shock models are consistent with previous measurements. These observations yield only weak evidence in favor of the predictions of shock models of molecule formation. Publication: The Astrophysical Journal Pub Date: July 1991 DOI: 10.1086/170227 Bibcode: 1991ApJ...375..642H Keywords: Hydrocarbons; Interstellar Matter; Line Spectra; Shock Wave Propagation; Astronomical Models; Line Shape; Radial Velocity; Astrophysics; INTERSTELLAR: MOLECULES; LINE PROFILES; MOLECULAR PROCESSES; RADIAL VELOCITIES; SHOCK WAVES full text sources ADS | data products SIMBAD (7)

CN, CH, and CH(+) toward Zeta Ophiuchi

Observations with a resolution of 600,000 of interstellar absorption from the CN 3874.6 A, CH 4300.3 A, and CH(+) 4232.5 A lines reveal several new features of the clouds along the line of sight toward Zeta Oph. The CN line consists of two overlapping components which are similar to those seen in the CO pure rotational lines. The CH(+) line is well described by a single Gaussian line profile with FWHM of 3.5 km/s. The CH profile is a composite of a CN-like profile and a CH(+)-like profile, indicating for the first time that CH exists in two regions of very different character. 35 refs.

Observations of the (1,0) vibrational band of interstellar CN toward Zeta Ophiuchi

Very high SNR, high-resolution observations of the 3580 A spectral region toward Zeta Oph have been obtained in an effort to detect the weak R(0) line corresponding to the (1,0) vibrational band of interstellar CN. The measurement of 0.67 + or - 0.06 mA for the CN (1,0) R(0) line strength indicates a J = 0 column density which is consistent with earlier determinations from the much stronger (0,0) R(0) line and the assumption of a single-component line profile. This finding implies that the complex velocity structure evident from CO radio observations of the Zeta Oph line of sight does not seriously complicate the saturation corrections for the CN lines. The Zeta Oph observations also reveal an equivalent width of 2.14 + or - 0.08 mA for the (3,0) R(0) line of interstellar (C-12)H(+) at 3579.02 A along with strong evidence of Cr I 3578.69 absorption. 44 refs.