Search

A high resolution spectrum of FTS sunspot umbra of NSO/Kitt Peak was used to conduct a search for the molecular absorption lines due to BeH, BeD and BeT isotopomers. Analysis led to estimates of identification of the molecular lines of bands A - X (0,0), (1,1) and (2,2) for BeH, A - X (0,0), (1,1), (2,2) and (3,3) for BeD and of A - X (0,0), (1,1) and (2,2) for BeT. Among the identified lines, those which are well resolved were selected for measurements to calculate equivalent widths. The values of effective rotational temperature T were estimated for bands A - X(1,1) and (2,2) of BeH, A - X(1,1) of BeD and A - X(2,2) of BeT to be 4228K, 4057K, 3941K and 3243K respectively.

Aims. We aim to investigate the physical and chemical properties of the molecular envelope of the oxygen-rich AGB star IK Tau. Methods. We carried out a millimeter wavelength line survey between ~79 and 356 GHz with the IRAM-30m telescope. We analysed the molecular lines detected in IK Tau using the population diagram technique to derive rotational temperatures and column densities. We conducted a radiative transfer analysis of the SO2 lines, which also helped us to verify the validity of the approximated method of the population diagram for the rest of the molecules. Results. For the first time in this source we detected rotational lines in the ground vibrational state of HCO+, NS, NO, and H2CO, as well as several isotopologues of molecules previously identified, namely, C18O, Si17O, Si18O, 29SiS, 30SiS, Si34S, H13CN, 13CS, C34S, H2 34S, 34SO, and 34SO2. We also detected several rotational lines in vibrationally excited states of SiS and SiO isotopologues, as well as rotational lines of H2O in the vibrationally excited state v2 = 2. We have also increased the number of rotational lines detected of molecules that were previously identified toward IK Tau, including vibrationally excited states, enabling a detailed study of the molecular abundances and excitation temperatures. In particular, we highlight the detection of NS and H2CO with fractional abundances of f (NS) ~ 10-8 and f (H2CO) ~ [10-7-10-8]. Most of the molecules display rotational temperatures between 15 and 40 K. NaCl and SiS isotopologues display rotational temperatures higher than the average (~65 K). In the case of SO2 a warm component with Trot ~ 290K is also detected. Conclusions. With a total of ~350 lines detected of 34 different molecular species (including different isotopologues), IK Tau displays a rich chemistry for an oxygen-rich circumstellar envelope. The detection of carbon bearing molecules like H2CO, as well as the discrepancies found between our derived abundances and the predictions from chemical models for some molecules, highlight the need for a revision of standard chemical models. We were able to identify at least two different emission components in terms of rotational temperatures. The warm component, which is mainly traced out by SO2, is probably arising from the inner regions of the envelope (at .8 R*) where SO2 has a fractional abundance of f (SO2) = 10-6. This result should be considered for future investigation of the main formation channels of this, and other, parent species in the inner winds of O-rich AGB stars, which at present are not well reproduced by current chemistry models. [ABSTRACT FROM AUTHOR]

Background We present results of our dense spectroscopic monitoring of Nova V5668 Sgr. Materials and Methods Starting on March 19, 2015, only a few days after its discovery, we have obtained a series of spectra with the Telescopio Internacional en Guanajuato, Robótico y Espectroscópico telescope and its Heidelberg extended range optical spectrograph échelle spectrograph, which offers a resolution of R = 20,000 and covers the optical wavelength range 3,8008,800 Å. We performed a line identification of the discernible features for four spectra, which are representative of the respective phases in the light curve evolution of that nova. We simultaneously analyzed the variations in the visual light curve and the corresponding spectra of Nova V5668 Sgr. Results We found that, during the declining phases of the nova, the absorption features in all hydrogen and many other lines had shifted to higher expansion velocities of about -2,000 km s−1. Conversely, during the rise toward the following maximum, these observed absorption features had returned to lower expansion velocities. We found that the absorption features of some Fe II lines displayed the same behavior, but in addition disappeared for a few days during some declining phases. Features of several N I lines also disappeared, while new N II lines appeared in the emission for a few days during some of the declining phases of the light curve of Nova V5668 Sgr. The shape of the emission features is changing during the evolution, and shows a clear double-peak structure after the deep minimum. Conclusions Thanks to the dense spectral monitoring we could observe several interesting developments of the Nova V5668 Sgr. [ABSTRACT FROM AUTHOR]

A detailed search for emission and absorption lines and an assessment of their upper limits are performed for Suzaku data. The method utilizes a matched-filtering approach to maximize the signal-to-noise ratio for a given energy resolution, which could be applicable to many types of line search. We first applied it to well-known active galactic nuclei spectra that have been reported to have ultra-fast outflows, and find that our results are consistent with previous findings at the ∼3σ level. We proceeded to search for emission and absorption features in two bright magnetars 4U 0142+61 and 1RXS J1708-4009, applying the filtering method to Suzaku data. We found that neither source showed any significant indication of line features, even using long-term Suzaku observations or dividing their spectra into spin phases. The upper limits on the equivalent width of emission/absorption lines are constrained to be a few eV at ∼1 keV and a few hundreds of eV at ∼10 keV. This strengthens previous reports that persistently bright magnetars do not show proton cyclotron absorption features in soft X-rays and, even if they exist, they would be broadened or much weaker than below the detection limit of X-ray CCD. [ABSTRACT FROM AUTHOR]

We present multi-epoch near-infrared observations of Nova Ophiuchi 2015 which was discovered during outburst in March 2015. This nova showed a few special properties viz. (i) it displayed an unusual prolonged flat-top light curve which does not easily fit into known classes of nova light curves, (ii) it showed evidence for possessing an evolved secondary in the outbursting binary system, and (iii) it made a rare reverse hybrid transition from the He/N class to Fe II class early during its outburst. The present studies focus on the spectroscopic evolution of the object around maximum light and early decline. We show that there was a unique, rapid strengthening and decline in the He 1.0831, 2.0581 µm line strengths during this stage, wherein the nova combined the traits of both the He/N and Fe II classes. Possible causes for this behaviour are discussed. The relative strengths of the Lyβ fluoresced OI 0.8446, 1.1287 µm lines are used to estimate the reddening to the nova. A recombination Case B analysis of the early spectra is used to set constraints on the electron density and emission measure, and a later time spectrum when the ejecta were optically thin is used to estimate the ejecta mass to be (0.95-1.9) × 10-4 M⊙. Power-law fits made to study the evolution of the continuum, show a fairly constant slope which differs from the trend generally expected during a nova's evolution viz. beginning with a blackbody and evolving to a free-free distribution at later stages. [ABSTRACT FROM AUTHOR]

Wavefunctions were determined using the multi-configuration Dirac-Hartree-Fock method. The core-core, core-valence, valence correlation, Breit interaction and quantum electrodynamics effects, as well as some higher-order correlation effects, were considered to obtain accurate wavelengths (λ), oscillator strengths (gf) and transition rates (A) of 2s²2p² - 2s2p³, 2s2p³ - 2s²2pnl (n ≥ 3) and 2s2p³ - 2s2p²3s E1 transitions. The branching ratio of 2s2p³ 5So2 (namely Aλ2143.45/Aλ2139.68) based on the latest calculation of 2.462 ± 0.119 is recommended for the determination of a nebula's electron temperature and electron density. The largest calculated gf value of 2s2p³ - 2s²2p4p is λ630.65, differing from that of λ1060.2 (i.e. 2s2p³ ³Po2 - 2s²2p4p ³S1) that was observed with the largest intensities in the Orion Nebula spectrum. In addition, the energy levels and the splittings of 2s2p³, the extremely difficult calculations of the rates of two-electron one-photon transitions as well as those of the very small intercombination A of 2s2p³ 5So2 were studied in detail. Because of the weak spin-orbit interaction, accurately calculating the levels ³Po1,2,0 (or ³Do3,2,1) and their transition matrix elements is very sensitive to relativistic and electron correlation effects. A special case for this is when the transition operators synchronously applied to wavefunctions with regard to 2s2p³ ³Po and 2s²2pnl (n = 4) become extremely sensitive to some higher-order correlation effects. [ABSTRACT FROM AUTHOR]

Wavefunctions were determined using the multi-configuration Dirac-Hartree-Fock method. The core-core, core-valence, valence correlation, Breit interaction and quantum electrodynamics effects, as well as some higher-order correlation effects, were considered to obtain accurate wavelengths (λ), oscillator strengths (gf) and transition rates (A) of 2s²2p² - 2s2p³, 2s2p³ - 2s²2pnl (n ≥ 3) and 2s2p³ - 2s2p²3s E1 transitions. The branching ratio of 2s2p³ 5So2 (namely Aλ2143.45/Aλ2139.68) based on the latest calculation of 2.462 ± 0.119 is recommended for the determination of a nebula's electron temperature and electron density. The largest calculated gf value of 2s2p³ - 2s²2p4p is λ630.65, differing from that of λ1060.2 (i.e. 2s2p³ ³Po2 - 2s²2p4p ³S1) that was observed with the largest intensities in the Orion Nebula spectrum. In addition, the energy levels and the splittings of 2s2p³, the extremely difficult calculations of the rates of two-electron one-photon transitions as well as those of the very small intercombination A of 2s2p³ 5So2 were studied in detail. Because of the weak spin-orbit interaction, accurately calculating the levels ³Po1,2,0 (or ³Do3,2,1) and their transition matrix elements is very sensitive to relativistic and electron correlation effects. A special case for this is when the transition operators synchronously applied to wavefunctions with regard to 2s2p³ ³Po and 2s²2pnl (n = 4) become extremely sensitive to some higher-order correlation effects. [ABSTRACT FROM AUTHOR]

We present deep spectroscopy of three Galactic planetary nebulae (PNe) with large abundance discrepancy factors: NGC 6153, M 1-42 and Hf 2-2. The spectra were obtained with Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph and cover the whole optical range (3040-11 000 Å) with a spectral resolution of ~20 000. For all three PNe, several hundred emission lines were detected and identified, with more than 70 per cent of them as permitted lines. Most of these permitted lines are excited by recombination. Numerous weak optical recombination lines (ORLs) of OII, CII, NII and Ne II were detected in the spectra and accurate fluxes measured. Line flux tables were compiled and ready for use by the community of nebular astrophysics. These ORLs were critically analysed using the effective recombination coefficients recently calculated for the optical recombination spectrum of NII and OII under the physical conditions of photoionized gaseous nebulae. Plasma diagnostics based on the heavy element ORLs were carried out using the new atomic data. Elemental abundances derived from the ORLs were systematically higher than those derived from the collisionally excited lines (CELs) by a factor of ~11, 22 and 80 for NGC 6153, M 1-42 and Hf 2-2, respectively. The electron temperatures derived from the heavy element ORLs are systematically lower than those derived from the CELs. These ORL versus CEL abundance and temperature discrepancies, previously observed in the three PNe through deep spectroscopy with medium to low spectral resolution, are thus confirmed by our analysis of the deep echelle spectra using the new atomic data. [ABSTRACT FROM AUTHOR]

Context. Deuterated forms of CH3+ are thought to be responsible for deuterium enrichment in lukewarm astronomical environments. There is no unambiguous detection of CH2D+ in space to date. Aims. Four submillimetre rotational lines of CH2D+ are documented in the literature. Our aim is to present a complete dataset of highly resolved rotational lines, including millimetre (mm) lines needed for a potential detection. Methods. We used a low-temperature ion trap and applied a novel IR–mm-wave double resonance method to measure the rotational lines of CH2D+. Results. We measured 21 low-lying (J ≤ 4) rotational transitions of CH2D+ between 23 GHz and 1.1 THz with accuracies close to 2 ppb. [ABSTRACT FROM AUTHOR]

Context. Deuterated forms of CH3+ are thought to be responsible for deuterium enrichment in lukewarm astronomical environments. There is no unambiguous detection of CH2D+ in space to date. Aims. Four submillimetre rotational lines of CH2D+ are documented in the literature. Our aim is to present a complete dataset of highly resolved rotational lines, including millimetre (mm) lines needed for a potential detection. Methods. We used a low-temperature ion trap and applied a novel IR–mm-wave double resonance method to measure the rotational lines of CH2D+. Results. We measured 21 low-lying (J ≤ 4) rotational transitions of CH2D+ between 23 GHz and 1.1 THz with accuracies close to 2 ppb. [ABSTRACT FROM AUTHOR]

We present results of a search for the 3.5 keV emission line in our recent very long (~ 1.4 Ms) XMM-Newton observation of the Draco dwarf spheroidal galaxy. The astrophysical X-ray emission from such dark matter-dominated galaxies is faint, thus they provide a test for the dark matter origin of the 3.5 keV line previously detected in other massive, but X-ray bright objects, such as galaxies and galaxy clusters. We do not detect a statistically significant emission line from Draco; this constrains the lifetime of a decaying dark matter particle to π >(7-9) × 1027 s at 95 per cent CL (combining all three XMM-Newton cameras; the interval corresponds to the uncertainty of the dark matter column density in the direction of Draco). The PN camera, which has the highest sensitivity of the three, does show a positive spectral residual (above the carefully modelled continuum) at E = 3.54 ± 0.06 keV with a 2.3σ significance. The two MOS cameras show less-significant or no positive deviations, consistently within 1σ with PN. Our Draco limit on π is consistent with previous detections in the stacked galaxy clusters, M31 and the Galactic Centre within their 1 - 2σ uncertainties, but is inconsistent with the high signal from the core of the Perseus cluster (which has itself been inconsistent with the rest of the detections). We conclude that this Draco observation does not exclude the dark matter interpretation of the 3.5 keV line in those objects. [ABSTRACT FROM AUTHOR]

Context. Despite the fact that many sulfur-bearing molecules, ranging from simple diatomic species up to astronomical complex molecules, have been detected in the interstellar medium, the sulfur chemistry in space is largely unknown and a depletion in the abundance of S-containing species has been observed in the cold, dense interstellar medium. The chemical form of the missing sulfur has yet to be identified. Aims. For these reasons, in view of the fact that there is a large abundance of triatomic species harbouring sulfur, oxygen, and hydrogen, we decided to investigate the HSO radical in the laboratory to try its astronomical detection. Methods. High-resolution measurements of the rotational spectrum of the HSO radical were carried out within a frequency range well up into the THz region. Subsequently, a rigorous search for HSO in the two most studied high-mass star-forming regions, Orion KL and Sagittarius (Sgr) B2, and in the cold dark cloud Barnard 1 (B1-b) was performed. Results. The frequency coverage and the spectral resolution of our measurements allowed us to improve and extend the existing dataset of spectroscopic parameters, thus enabling accurate frequency predictions up to the THz range. These were used to derive the synthetic spectrum of HSO, by means of the MADEX code, according to the physical parameters of the astronomical source under consideration. For all sources investigated, the lack of HSO lines above the confusion limit of the data is evident. Conclusions. The derived upper limit to the abundance of HSO clearly indicates that this molecule does not achieve significant abundances in either the gas phase or in the ice mantles of dust grains. [ABSTRACT FROM AUTHOR]

The L1544 prestellar core has been observed as part of the ASAI IRAM Large Program at 3 mm. These observations led to the detection of many complex molecules. In this Letter, we report the detection of two lines, at 85.5 GHz (40,4–30,3) and 106.9 GHz (50,5–40,4), respectively, of the protonated carbon dioxide ion, HOCO+. We also report the tentative detection of the line at 100.4 GHz (50,5–40,4) of DOCO+. The non-LTE analysis of the detected lines shows that the HOCO+ emission originates in the external layer where non-thermal desorption of other species has previously been observed. Its abundance is (5 ± 2) × 10-11. Modelling of the chemistry involved in the formation and destruction of HOCO+ provides a gaseous CO2 abundance of 2 × 10-7 (with respect to H2) with an upper limit of 2 × 10-6. [ABSTRACT FROM AUTHOR]

Context. The determination of isotopic ratios in interstellar molecules is a powerful probe of chemical routes leading to their formation. In particular, the 14N/ 15N abundance ratio of nitrogen-bearing species provides information on possible fractionation mechanisms. Up to now there is no accurate determination of this ratio in the interstellar medium (ISM) for the amidogen radical, NH2. Aims. This work is aimed at determining rotational frequencies of 15NH2 to enable its astronomical detection, which will help to understand the formation mechanisms of nitrogen hydrides in the ISM. Methods. We performed complementary measurements using both synchrotron-based, broadband far-infrared and high-resolution, submillimeter-wave frequencies to investigate the pure rotational spectrum of the 15NH2 species. Results. The first spectroscopic study of the 15N-isotopologue of the amidogen radical yielded an accurate set of molecular parameters. Conclusions. Accurate frequencies are now available for 15NH2 up to 7 THz (with N″≤ 13) allowing dedicated astronomical searches to be undertaken. [ABSTRACT FROM AUTHOR]

Aims. The recent discovery of methyl isocyanate (CH3NCO) in Sgr B2(N) and Orion KL makes methyl cyanate (CH3OCN) a potential molecule in the interstellar medium. The aim of this work is to fulfill the first requirement for its unequivocal identification in space, i.e. the availability of transition frequencies with high accuracy. Methods. The room-temperature rotational spectrum of methyl cyanate was recorded in the millimeter wave domain from 130 to 350 GHz. All rotational transitions revealed A-E splitting owing to methyl internal rotation and were globally analyzed using the ERHAM program. Results. The data set for the ground torsional state of methyl cyanate exceeds 700 transitions within J" = 10−35 and K" a = 0−13 and newly derived spectroscopic constants reproduce the spectrum close to the experimental uncertainty. Spectral features of methyl cyanate were then searched for in Orion KL, Sgr B2(N), B1-b, and TMC-1 molecular clouds. Upper limits to the column density of methyl cyanate are provided. [ABSTRACT FROM AUTHOR]

In this paper, we report the results of spectroscopic and photometric observations of the candidate evolved massive star MN48 disclosed via detection of a mid-infrared circular shell around it with the Spitzer Space Telescope. Follow-up optical spectroscopy of MN48 with the Southern African Large Telescope (SALT) carried out in 2011-2015 revealed significant changes in the spectrum of this star, which are typical of luminous blue variables (LBVs). The LBV status of MN48 was further supported by photometric monitoring which shows that in 2009-2011 this star has brightened by ≈0.9 and 1 mag in the V and Ic bands, respectively, then faded by ≈1.1 and 1.6 mag during the next four years, and apparently started to brighten again recently. The detected changes in the spectrum and brightness of MN48 make this star the 18th known Galactic bona fide LBV and increase the percentage of LBVs associated with circumstellar nebulae to more than 70 per cent. We discuss the possible birth place of MN48 and suggest that this star might have been ejected either from a putative star cluster embedded in the HII region IRAS 16455-4531 or the young massive star cluster Westerlund 1. [ABSTRACT FROM AUTHOR]

OH megamasers (OHMs) are rare, luminous molecular masers that are typically observed in (ultra) luminous infrared galaxies and serve as markers of major galaxy mergers. In blind emission line surveys such as the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA) survey for neutral hydrogen (H I), OHMs at z ~ 0.2 can mimic z ~ 0.05 H I lines. We present the results of optical spectroscopy of ambiguous H I detections in the ALFALFA 40 per cent data release detected by the Wide Field Infrared Survey Explorer (WISE) but with uncertain optical counterparts. The optical redshifts, obtained from observations at the Apache Point Observatory, revealed five new OHMs and identified 129 H I optical counterparts. 60 candidates remain ambiguous. The new OHMs are the first detected in a blind spectral line survey. The number of OHMs in ALFALFA is consistent with predictions from the OH luminosity function. Additionally, the mid-infrared magnitudes and colours of the OHM host galaxies found in a blind survey do not seem to differ from those found in previous targeted surveys. This validates the methods used in previous IR-selected OHM surveys and indicates there is no previously unknown OHM-producing population at z ~ 0.2. We also provide a method for future surveys to separate OH megamasers from 99 per cent of H I line emitters without optical spectroscopy by using WISE infrared colours and magnitudes. Since the fraction of OHMs found in flux-limited H I surveys is expected to increase with the survey's redshift, this selection method can be applied to future flux-limited high-redshift hydrogen surveys. [ABSTRACT FROM AUTHOR]

Context. For the spectral analysis of high-resolution and high signal-to-noise (S/N) 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 Kr iv–vii oscillator strengths for a large number of lines enable us to construct more detailed model atoms for our NLTE model-atmosphere calculations. This enables us to search for additional Kr lines in observed spectra and to improve Kr abundance determinations. Methods. We calculated Kr iv–vii 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 S/N ultraviolet (UV) observations of the hot white dwarf RE 0503−289. Results. We reanalyzed the effective temperature and surface gravity and determined Teff = 70000 ± 2000 K and log (g/ cm s-2) = 7.5 ± 0.1. We newly identified ten Kr v lines and one Kr vi line in the spectrum of RE 0503−289. We measured a Kr abundance of −3.3 ± 0.3 (logarithmic mass fraction). We discovered that the interstellar absorption toward RE 0503−289 has a multi-velocity structure within a radial-velocity interval of −40 km s-1

Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed and new findings suggest that these fullerenes may possibly form from polycyclic aromatic hydrocarbons (PAHs) in the ISM. Moreover, the first confirmed identification of two strong diffuse interstellar bands (DIBs) with the fullerene, C60+, connects the long standing suggestion that various fullerenes could be DIB carriers. These new discoveries justify reassessing the overall importance of interstellar fullerene compounds, including fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerene compounds is complex. In addition to fullerene formation in grain shattering, fullerene formation from fully dehydrogenated PAHs in diffuse interstellar clouds could perhaps transform a significant percentage of the tail of low-mass PAH distribution into fullerenes including EEHFs. But many uncertain processes make it extremely difficult to assess their expected abundance, composition and size distribution, except for the substantial abundance measured for C60+. EEHFs share many properties with pure fullerenes, such as C60, as regards stability, formation/destruction and chemical processes, as well as many basic spectral features. Because DIBs are ubiquitous in all lines of sight in the ISM, we address several questions about the interstellar importance of various EEHFs, especially as possible carriers of diffuse interstellar bands. Specifically, we discuss basic interstellar properties and the likely contributions of fullerenes of various sizes and their charged counterparts such as C60+, and then in turn: 1) metallofullerenes; 2) heterofullerenes; 3) fulleranes; 4) fullerene-PAH compounds; 5) H2@C60. From this reassessment of the literature and from combining it with known DIB line identifications, we conclude that the general landscape of interstellar fullerene compounds is probably much richer than heretofore realized. EEHFs, together with pure fullerenes of various sizes, have many properties necessary to be suitably carriers of DIBs: carbonaceous nature; stability and resilience in the harsh conditions of the ISM; existing with various heteroatoms and ionization states; relatively easy formation; few stable isomers; spectral lines in the right spectral range; various and complex energy internal conversion; rich Jahn-Teller fine structure. This is supported by the first identification of a DIB carrier as C60+. Unfortunately, the lack of any precise information about the complex optical spectra of EEHFs and most pure fullerenes other than C60 and about their interstellar abundances still precludes definitive assessment of the importance of fullerene compounds as DIB carriers. Their compounds could significantly contribute to DIBs, but it still seems difficult that they are the only important DIB carriers. Regardless, DIBs appear as the most promising way of tracing the interstellar abundances of various fullerene compounds if the breakthrough in identifying C60+ as a DIB carrier can be extended to more spectral features through systematic studies of their laboratory gas-phase spectroscopy. [ABSTRACT FROM AUTHOR]

Context. Recent findings of line emission at 3.5 keV in both individual and stacked X-ray spectra of galaxy clusters have been speculated to have dark matter origin. Aims. If the origin is indeed dark matter, the emission line is expected to be detectable from the Milky Way dark matter halo. Methods. We perform a line search in public Chandra X-ray observations of the region near Sgr A*. We derive upper limits on the line emission flux for the 2.0−9.0 keV energy interval and discuss their potential physical interpretations including various scenarios of decaying and annihilating dark matter. Results. While we find no clear evidence for its presence, the upper flux limits are not inconsistent with the recent detections for conservative mass profiles of the Milky Way. Conclusions. The results depend mildly on the spectral modelling, and strongly on the choice of dark matter profile. [ABSTRACT FROM AUTHOR]

We searched for an X-ray line at energies around 3.5 keV in deep, ~1.6 Ms XMM-Newton observations of the dwarf spheroidal galaxy Draco. No line was found in either the Metal Oxide Semi-conductor (MOS) or the p-type/n-type semiconductor (PN) detectors. The data in this energy range are completely consistent with a single, unfolded power-law modelling the particle background, which dominates at these energies, plus instrumental lines; the addition of a ~3.5 keV line feature gives no improvement to the fit. The corresponding upper limit on the line flux rules out a dark matter decay origin for the 3.5 keV line found in observations of clusters of galaxies and in the Galactic Centre at greater than 99 per cent confidence level. [ABSTRACT FROM AUTHOR]

Context. Dimethyl sulfide, CH3SCH3 (DMS), is a nonrigid, sulfur-containing molecule whose astronomical detection is considered to be possible in the interstellar medium. Very accurate spectroscopic constants were obtained by a laboratory analysis of rotational microwave and millimeter wave spectra, as well as rotation-torsional far-infrared (FIR) spectra, which can be used to predict transition frequencies for a detection in interstellar sources. Aims. This work aims at the experimental study and theoretical analysis of the ground torsional state and ground torsional band ν15 of DMS in a large spectral range for astrophysical use. Methods. The microwave spectrum was measured in the frequency range 2−40 GHz using two Molecular Beam Fourier Transform MicroWave (MB-FTMW) spectrometers in Aachen, Germany. The millimeter spectrum was recorded in the 50-110 GHz range. The FIR spectrum was measured for the first time at high resolution using the FT spectrometer and the newly built cryogenic cell at the French synchrotron SOLEIL. Results. DMS has two equivalent methyl internal rotors with a barrier height of about 730 cm-1 . We performed a fit, using the XIAM and BELGI-Cs-2Tops codes, that contained the new measurements and previous transitions reported in the literature for the ground torsional state νt = 0 (including the four torsional species AA, AE, EA and EE) and for the ground torsional band ν15 = 1 ← 0 (including only the AA species). In the microwave region, we analyzed 584 transitions with J ≤ 30 of the ground torsional state νt = 0 and 18 transitions with J ≤ 5 of the first excited torsional state νt = 1. In the FIR range, 578 transitions belonging to the torsional band ν15 = 1 ← 0 with J ≤ 27 were assigned. Totally, 1180 transitions were included in a global fit with 21 accurately determined parameters. These parameters can be used to produce a reliable line-list for an astrophysical detection of DMS. [ABSTRACT FROM AUTHOR]

Detections of C60 and C70 fullerenes in planetary nebulae (PNe) of the Magellanic Clouds and of our own Galaxy have raised the idea that other forms of carbon, such as hydrogenated fullerenes (fulleranes like C60H36 and C60H18), buckyonions, and carbon nanotubes, may be widespread in the Universe. Here we present VLT/ISAAC spectra (R ~ 600) in the 2.9-4.1 μm spectral region for the Galactic PNe Tc 1 and M 1-20, which have been used to search for fullerene-based molecules in their fullerene-rich circumstellar environments. We report the non-detection of the most intense infrared bands of several fulleranes around ~3.4-3.6 μm in both PNe. We conclude that if fulleranes are present in the fullerene-containing circumstellar environments of these PNe, then they seem to be much less abundant than C60 and C70. Our non-detections, together with the (tentative) fulleranes detection in the proto-PN IRAS 01005+7910, suggest that fulleranes may be formed in the short transition phase between AGB stars and PNe, but they are quickly destroyed by the UV radiation field from the central star. [ABSTRACT FROM AUTHOR]

We present direct spectroscopic modelling of 11 high signal-to-noise ratio observed spectra of the Type Ia supernova (SN) 2010kg, taken between-10 and+5 d with respect to B-maximum. The synthetic spectra, calculated with the SYN++ code, span the range between 4100 and 8500 Å. Our results are in good agreement with previous findings for other Type Ia SNe. Most of the spectral features are formed at or close to the photosphere, but some ions, like Fe II and MgII, also form features at ~2000-5000 km s-1 above the photosphere. The well-known high-velocity features of the Ca II IR-triplet as well as Si II λ6355 are also detected. The single absorption feature at ~4400 Å, which usually has been identified as due to Si III, is poorly fit with Si III in SN 2010kg. We find that the fit can be improved by assuming that this feature is due to either C III or OII, located in the outermost part of the ejecta, ~4000-5000 km s-1 above the photosphere. Since the presence of CIII is unlikely, because of the lack of the necessary excitation/ionization conditions in the outer ejecta, we identify this feature as due to O II. The simultaneous presence of O I and O II is in good agreement with the optical depth calculations and the temperature distribution in the ejecta of SN 2010kg. This could be the first identification of singly ionized oxygen in a Type Ia SN atmosphere. [ABSTRACT FROM AUTHOR]

I present the automated line fitting algorithm, ALFA, a new code which can fit emission line spectra of arbitrary wavelength coverage and resolution, fully automatically. In contrast to traditional emission line fitting methods which require the identification of spectral features suspected to be emission lines, ALFA instead uses a list of lines which are expected to be present to construct a synthetic spectrum. The parameters used to construct the synthetic spectrum are optimized by means of a genetic algorithm. Uncertainties are estimated using the noise structure of the residuals. An emission line spectrum containing several hundred lines can be fitted in a few seconds using a single processor of a typical contemporary desktop or laptop PC. I show that the results are in excellent agreement with those measured manually for a number of spectra. Where discrepancies exist, the manually measured fluxes are found to be less accurate than those returned by ALFA. Together with the code NEAT, ALFA provides a powerful way to rapidly extract physical information from observations, an increasingly vital function in the era of highly multiplexed spectroscopy. The two codes can deliver a reliable and comprehensive analysis of very large data sets in a few hours with little or no user interaction. [ABSTRACT FROM AUTHOR]

We detect variability of the Fe Ka emission line in the spectrum of X-ray pulsar 4U 1626-67, correlated with changes in its luminosity and in the shape of its pulse profile. Analysis of archival Chandra and RXTE observations revealed the presence of an intrinsically narrow Fe Ka emission line in the spectrum obtained during the source's current high-luminosity period. However, the line was not present during an XMM-Newton observation seven years earlier, when the source was ~three times fainter. The line is resolved by the high-energy grating of Chandra at the 98 per cent confidence level, and its small intrinsic width, s = 36.4+15.3 -11.3 eV, suggests reflection off an accretion disc at the radius R (7.5+8.2 -3.8) 108 cm assuming a Keplerian disk, viewed at an inclination angle of 20?. This value is consistent with the radius of the magnetosphere of the pulsar, suggesting that the line originates near the inner edge of a disc that is truncated by the magnetic field of the neutron star. Timing analysis of the XMM-Newton and RXTE data revealed a major change in the pulse profile of the source from a distinct double-peaked shape during the high-luminosity state when the line was present, to a much more complex multipeak structure during the low-luminosity state. We argue that the appearance of the line and the change in the shape of the pulse profile are correlated and are the result of a major change in the emission diagram of the accretion column, from a pencil-beam pattern at low luminosity, to a fan-beam pattern at high luminosity. [ABSTRACT FROM AUTHOR]

Next-generation spectroscopic surveys will map the large-scale structure of the observable universe, using emission line galaxies as tracers. While each survey will map the sky with a specific emission line, interloping emission lines can masquerade as the survey's intended emission line at different redshifts. Interloping lines from galaxies that are not removed can contaminate the power spectrum measurement, mixing correlations from various redshifts and diluting the true signal. We assess the potential for power spectrum contamination, finding that an interloper fraction worse than 0.2% could bias power spectrum measurements for future surveys by more than 10% of statistical errors, while also biasing power spectrum inferences. We also construct a formalism for predicting cosmological parameter measurement bias, demonstrating that a 0.15%-0.3% interloper fraction could bias the growth rate by more than 10% of the error, which can affect constraints on gravity from upcoming surveys. We use the COSMOS Mock Catalog (CMC), with the emission lines rescaled to better reproduce recent data, to predict potential interloper fractions for the Prime Focus Spectrograph (PFS) and the Wide-Field InfraRed Survey Telescope (WFIRST). We find that secondary line identification, or confirming galaxy redshifts by finding correlated emission lines, can remove interlopers for PFS. For WFIRST, we use the CMC to predict that the 0.2% target can be reached for the WFIRST Ha survey, but sensitive optical and near-infrared photometry will be required. For the WFIRST [OIII] survey, the predicted interloper fractions reach several percent and their effects will have to be estimated and removed statistically (e.g., with deep training samples). These results are optimistic as the CMC does not capture the full set of correlations of galaxy properties in the real Universe, and they do not include blending effects. Mitigating interloper contamination will be crucial to the next generation of emission line surveys. [ABSTRACT FROM AUTHOR]