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Thermal OH emission from IRC + 10216 in the 1665- and 1667-MHz lines has been searched for. No emission was detected, yielding an upper limit for the OH abundance in the envelope. Within the photodissociation region where OH is expected to occur, OH/CO is less than 2.7 x 10 exp -3.
The purpose of the grant was to obtain and analyze IUE (UV) and ground-based (optical) spectra of the central bar of NGC 4214, which contains several bright H II regions, in order to further explore the properties of the Wolf-Rayet stars in this galaxy. Several spatially distinct regions, with widely different equivalent widths of optical Wolf-Rayet lines, could be sampled by the large IUE entrance aperture. By using newly developed extraction techniques, the spectra of these H II regions could be isolated, and differences in their stellar populations would be systematically studied. Data were obtained with IUE in late February and early March, 1992. Some of the shifts were successful, but a few were not -- apparently the blind offset from the nearby star did not work equally well in all cases. Thus, the signal-to-noise ratio is somewhat lower than we had hoped. This necessitated a more careful extraction of the spectra of individual H II regions from the two-dimensional spectra. (A program that models the point spread function in the spatial direction was used to deblend the distinct H II regions.) The IUE data are currently being analyzed in conjunction with ground-based optical spectra. There appear to be obvious variations in the stellar population over angular scales of only a few arc seconds. The second part of the research performed under this grant was a continuation of a project that uses IUE (UV) and ground-based (optical) spectra to infer the physical conditions in Low-Ionization Nuclear Emission-Line Regions (LINER's). We have obtained spectra of a few key objects that cover a representative range in LINER continuum and emission-line properties. The overall goals are to (1) separate the emission into spatially distinct components, (2) establish whether the observed nuclear ultraviolet continua indicate sufficient photoionizing fluxes to account for the emission lines, (3) determine whether the nuclear emission can be explained by hot stars alone, (4) detect and measure the strengths of UV emission lines, and (5) search for systematic differences in the UV spectra of LINER's whose other properties differ in some respects.
This paper reports the initial results of the Palomar Transit Grism Survey (PTGS). The PTGS was designed to produce a sample of z greater than 2.7 quasars that were identified by well-defined selection criteria. The survey consists of six narrow (approximately equal to 8.5 min wide) strips of sky; the total effective area is 61.47 sq deg. Low-resolution slitless spectra, covering the wavelength range from 4400 to 7500 A, were obtained for approximately 600 000 objects. The wavelength- and flux-calibrated spectra were searched for emission lines with an automatic software algorithm. A total to 1655 emission features in the grism data satisfied our signal-to-noise ratio and equivalent width selection criteria; subsequent slit spectroscopy of the candidates confirmed the existence of 1052 lines (928 different objects). Six groups of emission lines were detected in the survey: Lyman alpha + N V, C IV, C III1, Mg II, H Beta + (O III), and H alpha + (S II). More than two-thirds of the candidates are low-redshift (z less than 0.45) emission-line galaxies; ninety objects are high-redshift quasars (z greater than 2.7) detected via their Lyman alpha + N V emission lines. The survey contains three previously unknown quasars brighter than 17th magnitude; all three have redshifts of approximately equal to 1.3. In this paper we present the observational properties of the survey, the algorithms used to select the emission-line candidates, and the catalog of emission-line objects.
The 7 s X-ray pulsator 1E 2259+586 was observed for approximately 1 day in 1993 with the Advanced Satellite for Cosmology and Astrophysics (ASCA). Observations were also obtained with Broad Band X-ray Telescope (BBXRT) in 1990 a few months after Ginga had observed 1E 2259+586 to be brighter than normal and the BBXRT data show 1E 2259+586 to be at an intermediate brightness level. By contrast, the ASCA data appear to have been obtained during a more common lower luminosity state. The pulse profiles we obtain are consistent with a connection between flux and pulse shape reported from Ginga data, and the pulsator continues to spin down. We use our high spectral resolution data to search for cyclotron lines in the spectrum that were claimed from observations made with other satellites. We find that the ASCA spectra of 1E 2259+586 cannot be satisfactorily fitted with either a single power law or a combination of two power laws, and that significant residuals occur around 1.5 and 5 keV. However, a combination of a power law and blackbody gives a good fit over the entire ASCA energy band with no evidence of spectral features. We have reanalyzed a Ginga LAC spectrum and find that this is also significantly better fitted by this two-component spectrum than a single power law. A possible explanation for such a two-component spectrum is that the blackbody emission comes from a neutron star and that the power-law component comes, at least in part, from a surrounding nebula. As there has, so far, no direct evidence that 1E 2259+586 is a binary system we consider whether there are other plausible mechanisms that might power the observed X-ray emission.
Our group has designed a heterodyne submillimeter receiver that offers a very wide IF bandwidth of 12 GHz, while still maintaining a low noise temperature. The 180-300 GHz double-sideband design uses a single SI5 device excited by a full bandwidth, fixed-tuned waveguide probe on a silicon substrate. The IF output frequency (limited by the MMIC low noise IF preamplifier) is 6-18 GHz. providing an instantaneous RF bandwidth of 24 GHz (double-sideband). Intensive simulations predict that the junction will achieve a conversion loss better than 1-2 dB and a mixer noise temperature of less than 20 K across the band (twice the quantum limit). The single sideband receiver noise temperature goal is 70 K. The wide instantaneous bandwidth and low noise will result in an instrument capable of a variety of important astrophysical and environmental observations beyond the capabilities of current instruments. Lab testing of the receiver will begin this summer, and first light on the CSO should be in the Spring of 2003. At the CSO, we plan to use receiver with WASP2, a wideband spectrometer, to search for spectral lines from SCUBA sources. This approach should allow us to rapidly develop a catalog of redshifts for these objects.
The reactive collision avoidance (RCA) algorithm allows a spacecraft to find a fuel-optimal trajectory for avoiding an arbitrary number of colliding spacecraft in real time while accounting for acceleration limits. In addition to spacecraft, the technology can be used for vehicles that can accelerate in any direction, such as helicopters and submersibles. In contrast to existing, passive algorithms that simultaneously design trajectories for a cluster of vehicles working to achieve a common goal, RCA is implemented onboard spacecraft only when an imminent collision is detected, and then plans a collision avoidance maneuver for only that host vehicle, thus preventing a collision in an off-nominal situation for which passive algorithms cannot. An example scenario for such a situation might be when a spacecraft in the cluster is approaching another one, but enters safe mode and begins to drift. Functionally, the RCA detects colliding spacecraft, plans an evasion trajectory by solving the Evasion Trajectory Problem (ETP), and then recovers after the collision is avoided. A direct optimization approach was used to develop the algorithm so it can run in real time. In this innovation, a parameterized class of avoidance trajectories is specified, and then the optimal trajectory is found by searching over the parameters. The class of trajectories is selected as bang-off-bang as motivated by optimal control theory. That is, an avoiding spacecraft first applies full acceleration in a constant direction, then coasts, and finally applies full acceleration to stop. The parameter optimization problem can be solved offline and stored as a look-up table of values. Using a look-up table allows the algorithm to run in real time. Given a colliding spacecraft, the properties of the collision geometry serve as indices of the look-up table that gives the optimal trajectory. For multiple colliding spacecraft, the set of trajectories that avoid all spacecraft is rapidly searched on-line. The optimal avoidance trajectory is implemented as a receding-horizon model predictive control law. Therefore, at each time step, the optimal avoidance trajectory is found and the first time step of its acceleration is applied. At the next time step of the control computer, the problem is re-solved and the new first time step is again applied. This continual updating allows the RCA algorithm to adapt to a colliding spacecraft that is making erratic course changes.
We present a sample of 45 Damped Ly-Alpha system [DLA; H I-N is greater than or equal to 2 x 10(exp. 20) cm(exp. -2)] counterparts (33 detections, 12 upper limits) which host gamma-ray bursts (GRB-DLAs) in order to investigate star formation and metallicity within galaxies hosting DLAs. Our sample spans z is approx. 2 - 6 and is nearly three times larger than any previously detected DLA counterparts survey based on quasar line-of-sight searches (QSO-DLAs). We report star formation rates (SFRs) from rest-frame UV photometry and spectral energy distribution modeling. We find that DLA counterpart SFRs are not correlated with either redshift or H I column density. Thanks to the combination of Hubble Space Telescope and ground-based observations, we also investigate DLA host star formation efficiency. Our GRB-DLA counterpart sample spans both higher efficiency and low efficiency star formation regions compared to the local Kennicutt-Schmidt relation, local star formation laws, and z is approximately 3 cosmological simulations. We also compare the depletion times of our DLA hosts sample to other objects in the local universe; our sample appears to deviate from the star formation efficiencies measured in local spiral and dwarf galaxies. Furthermore, we find similar efficiencies as local inner disks, SMC, and Lyman-break galaxy outskirts. Finally, our enrichment time measurements show a spread of systems with under- and over-abundance of metals, which may suggest that these systems had episodic star formation and a metal enrichment/depletion as a result of strong stellar feedback and/or metal inflow/outflow.
We present a high-contrast imaging search for Paβ line emission from protoplanets in the PDS 70 system with Keck/OSIRIS integral field spectroscopy. We applied the high-resolution spectral differential imaging technique to the OSIRIS J-band data but did not detect the Paβ line at the level predicted using the parameters of Hashimoto et al. (2020). This lack of Paβ emission suggests the MUSE-based study may have overestimated the line width of Hα. We compared our Paβ detection limits with the previous Hα flux and Hβ limits and estimated AV to be ∼0.9 and 2.0 for PDS 70 b and c, respectively. In particular, PDS 70 b’s AV is much smaller than implied by high-contrast near-infrared studies, which suggests the infrared-continuum photosphere and the hydrogen-emitting regions exist at different heights above the forming planet.
The focal plane crystal spectrometer (FPCS) on the Einstein Observatory has been used to perform a high-resolution spectroscopic search for oxygen X-ray line emission from four active galaxies: Fairall 9, Mrk 421, Mrk 501, and PKS 0548 - 322. Specifically, O VIII Ly-alpha and Ly-beta, whose unredshifted energies are 653 and 775 eV, respectively, were sought. No narrow-line emission was detected within the energy bands searched. Upper limits are calculated on the line flux from these sources of 30 eV equivalent width and use a photoionization model to place corresponding upper limits on the densities of diffuse gas surrounding the active nuclei. The upper limits on gas density range from about 0.02-50/cu cm and probe various radial distances from the central source. This is the first time high-resolution X-ray spectroscopy has been used to place constraints on the intercloud medium in active galaxies.
Free neutrons produced by nuclear reactions in high-temperature plasmas may undergo proton capture in ambient material, giving rise to gamma-ray emisison in a line at 2.223 MeV. Plausible settings for this process include accretion disks around black holes, material accreting onto neutron stars, and the binary companions of TeV gamma-ray sources. Data accumulated by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) between 1980 and 1989 have been searched for evidence of this line, during periods when the black hole candidates Cygnus X-1 and the Galactic center were in transit across the GRS aperture. During these periods the neutron-star X-ray binaries Cygnus X-3 and Scorpius X-1 were also in the respective GRS fields of view. A 3-sigma upper limit of 0.0001/sq cm s has been placed on the steady emission in the 2.223 MeV line from the Galactic center and Scorpius X-1. Upper limits in the range 0.00012-0.00022 gamma/sq cm s have been set for Cygnus X-1 according to different models of the origin of the emission. The 3-sigma upper limit to the phase-averaged steady emission from Cygnus X-3 was found to be 0.00012 gamma/sq cm s.
Dark matter particle annihilation or decay can produce monochromatic gamma-ray lines and contribute to the diffuse gamma-ray background. Flux upper limits are presented for gamma-ray spectral lines from 7 to 200 GeV and for the diffuse gamma-ray background from 4.8 GeV to 264 GeV obtained from two years of Fermi Large Area Telescope data integrated over most of the sky. We give cross section upper limits and decay lifetime lower limits for dark matter models that produce gamma-ray lines or contribute to the diffuse spectrum, including models proposed as explanations of the PAMELA and Fermi cosmic-ray data.
The IUE satellite has undertaken UV observations of the proto-planetary nebulae V1016 Cyg, HM Sge, and HBV 475, yielding emission line fluxes, line ratios, line profiles, electron densities, and distances from these objects. While levels of increasing excitation and ionization as a function of time are shown by the data for the first two nebulae, the trend for HBV 475 is found to lead in the opposite direction. The formation of a shell is suggested by dramatic changes in the HM Sge UV line profiles over the last four years, including the disappearance of W-R features and the incipient splitting of the semi-forbidden C III 1909 A line. An additional IUE search for UV variability in the planetary nebulae IC 4997 and NGC 6905 has yielded emission line fluxes, line ratios and profiles, and central star temperatures, as well as stratification effects data for several ions in NGC 6905
Far-ultraviolet spectra of the gravitational lens components Q0957+561 A and B were obtained with the Hubble Space Telescope Faint Object Spectrograph to investigate the characteristic dimension of Lyman-alpha forest clouds in the direction of the quasar. If one makes the usual assumption that the absorbing structures are spherical clouds with a single radius, that radius can be found analytically from the ratio of Lyman-alpha lines in only one line of sight to the number in both. A simple power series approximation to this solution, accurate everywhere to better than 1%, will be presented. Absorption lines in Q0957+561 having equivalent width greater than 0.3 A in the observer's frame not previously identified as interstellar lines, metal lines, or higher order Lyman lines were taken to be Ly-alpha forest lines. The existence of each line in this consistently selected set was then verified by its presence in two archival FOS spectra with approximately 1.5 times higher signal to noise than our spectra. Ly-alpha forest lines appear at 41 distinct wavelengths in the spectra of the two images. One absorption line in the spectrum of image A has no counterpart in the spectrum of image B, and one line in image B has no counterpart in image A. Based on the separation of the lines of sight over the redshift range searched for Ly-alpha forest lines, the density of the absorbing clouds in the direction of Q0957+561 must change significantly over a radius R = 160 (+120, -70) h (sup -1) (sub 50) kpc (H (sub 0) 50 h (sub 50) km s (sup -1) kpc (sup -1), q (sub 0) = 1/2). The 95% confidence interval on R extends from (50 950) h (sup -1) (sub 50) kpc.
For the spectral analysis of high-resolution and high signal-to-noise (SN) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Aims. New Krivvii oscillator strengths for a large number of lines enable us to construct more detailed model atoms for our NLTEmodel-atmosphere calculations. This enables us to search for additional Kr lines in observed spectra and to improve Kr abundance determinations. Methods. We calculated Krivvii oscillator strengths to consider radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Kr lines that are exhibited in high-resolution and high SN ultraviolet (UV)observations of the hot white dwarf RE 0503.
Uranium wavelengths in the spectra of Ap stars are studied to see if they give any indication of a recent r-process event. It is concluded that there is no credible evidence for an admixture of uranium-235 in these stars, which would imply such an event. The evidence, though negative, is badly confused by blending of lines, and a final judgement must wait for an observational clarification of the situation.
Archival high-dispersion spectra from the IUE are used in a search for Bowen emission lines of Fe II excited by the stronger transition of the O VI resonance doublet. The possibility of using these Fe II emission lines as a diagnostic of the strength of the far-ultraviolet emission of O VI at 1032 A is explored. It is found that the Fe II emission lines are quite common and strong in symbiotic stars, particularly those of the type known as 'symbiotic novae', as well as in normal novae. The lines are observed in central stars of some planetary nebulae of the O VI sequence besides a few central stars of type WR. High density, high excitation, and high temperature are suggested to be requirements for the excitation of the Fe II fluorescence lines. It is pointed out that while these lines were observed in PG 1159-035 and K1-16, they were not observed in AGNs.
The 2.12-micron line of molecular hydrogen was searched for in emission from a variety of southern hemisphere objects, including infrared sources associated with molecular clouds and H II regions, the galactic center, and three external galaxies. Negative results are reported for all sources.
Results are reported from a search for Fe VII absorption lines in data from high-dispersion IUE-SWP observations of PN nuclei (PNN), hot subdwarfs (HSDs), and hot white dwarfs (HWDs). The data-reduction techniques employed are outlined, and the results are presented in extensive tables and sample spectra and characterized in detail. Absorption in at least one of the four Fe VII lines above 120 nm wavelength is found in 22 of 51 PNN, and possibly in 10 HSDs, in the pulsating HWD PG 1159 - 035, and in the PNN K1 - 16. It is concluded that Fe VII is more common in WD progenitors such as PNN than previously predicted and is especially typical of the more luminous low-gravity stars.