Southern spectrophotometric standards.

We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2−10, Mkn 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253−0312, Tol 1457−262, Tol 1924−416 and the H ii region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10420Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C 2+ and/or O 2+ from faint pure recombination lines (RLs) in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O vs. O/H, C/O vs. N/O and C/N vs. O/H relations for Galactic and extragalactic H ii regions and comparing with results for halo stars and DLAs. We find that H ii regions in star-forming dwarf galaxies occupy a different locus in the C/O vs. O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H ii regions should have the same origin than in halo stars. The comparison between the C/O ratios in H ii regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H ii regions and that this coupling breaks in very low-metallicity objects.

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“…The standard stars LTT 3864, CD−32 • 9927, and EG 274 (Hamuy et al 1992(Hamuy et al , 1994 were observed to perform the flux calibration.…”

Section: Sample Selection Observations and Data Reductionmentioning

confidence: 99%

Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution★

Esteban

García‐Rojas

Carigi³

et al. 2014

Monthly Notices of the Royal Astronomical Society

111

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“…The final products of the pipeline were 2D wavelength calibrated spectra; our own IDL scripts were used thereafter to collapse the spectra in the spatial direction and obtain our final 1D-spectra. The standard star LTT 3218 (Hamuy et al 1992(Hamuy et al , 1994 was observed to perform the flux calibration and was also fully reduced with the pipeline. The flux calibration and radial velocity correction were performed using the standard procedures with IRAF 1 (Tody 1993).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

s-process enrichment in the planetary nebula NGC 3918. Results from deep echelle spectrophotometry

García‐Rojas¹,

Madonna²,

Luridiana³

et al. 2015

Mon. Not. R. Astron. Soc.

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The chemical content of the planetary nebula NGC 3918 is investigated through deep, highresolution (R∼40000) UVES at VLT spectrophotometric data. We identify and measure more than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr, Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up in NGC 3918s progenitor star. We find that Kr is strongly enriched in NGC 3918 and that Se is less enriched than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC 3918 as is Kr and, therefore, that neutron exposure is typical of modestly subsolar metallicity AGB stars. A clear correlation is found when representing [Kr/O] vs. log(C/O) for NGC 3918 and other objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought to the surface of AGB stars along with s-processed material during third dredge-up episodes, as predicted by nucleosynthesis models. We also detect numerous refractory element lines (Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C, N, O, and Ne. We compute physical conditions from a large number of diagnostics, which are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to the high ionization of NGC 3918 we detect a large number of recombination lines of multiple ionization stages of C, N, O and Ne. The abundances obtained for these elements by using recently-determined state-of-the-art ICF schemes or simply adding ionic abundances are in very good agreement, demonstrating the quality of the recent ICF scheme for high ionization planetary nebulae.

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“…An overview of the CN observations, along with the geometric circumstances, is presented in Table 1. Exposures were ranging from 300 to 1,200 s. Observations of standard stars (Hamuy et al 1992(Hamuy et al , 1994 were performed to calibrate the flux in the comet images.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Rotation of the Nucleus, Gas Kinematics and Emission Pattern of Comet 8P/Tuttle: Preliminary Results from Optical Imaging of the CN Coma

et al. 2009

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We present preliminary results of the narrow-band CN observations of comet 8P/Tuttle from early January 2008, realized as part of a project consisting of nearsimultaneous spectroscopic monitoring of HCN at millimeter-wavelengths and optical imaging of the coma. The mean-image subtraction method revealed low-contrast CN envelopes. Using the image cross-correlation technique we measured the projected velocity of these shells. For the sunward part we found it to be equal to 0.96 ± 0.03 km s -1 on January 4 and 1.10 ± 0.01 km s -1 on January 9, whereas the anti-sunward part reached 0.73 ± 0.05 and 0.80 ± 0.02 km s -1 , respectively. The periodicity of gas emission was investigated using a repeatability of the shells, their kinematics, and an aperture photometry of the near nucleus region. We found a period of 5.70 ± 0.07 h (along with multiples), consistent with previous findings by other authors. A toy Monte Carlo model was implemented to reproduce the time-series of the CN images. We show that emission of HCN into a relatively wide cone by a single active region on a rotating nucleus is the most probable scenario.Electronic supplementary material The online version of this article

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Southern spectrophotometric standards.

Cited by 535 publications

References 17 publications

Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution★

Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution★

s-process enrichment in the planetary nebula NGC 3918. Results from deep echelle spectrophotometry

Rotation of the Nucleus, Gas Kinematics and Emission Pattern of Comet 8P/Tuttle: Preliminary Results from Optical Imaging of the CN Coma

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