This paper examines, compares and plots optical, near- and mid-infrared (MIR) photometric data for 605 planetary nebulae (PNe) in the Large Magellanic Cloud (LMC). With the aid of multiwavelength ...surveys such as the Spitzer legacy programme Surveying the Agents of a Galaxy's Evolution, the Two Micron All Sky Survey and the Magellanic Cloud Photometric Survey, plots have been constructed to expose the relative contributions from molecular hydrogen, polycyclic aromatic hydrocarbons, forbidden emission lines, warm dust continuum and stellar emission at various bands. Besides identifying trends, these plots have helped to reveal PN mimics including six previously known PNe in the outer LMC which are re-classified as other object types. Together with continuing follow-up optical observations, the data have enabled a substantial reduction in the number of PNe previously tagged as 'likely' and 'possible'. The total number of LMC PNe is adjusted to 715 but with a greater degree of confidence in regard to classification. In each colour-colour plot, the more highly evolved LMC PNe are highlighted for comparison with younger, brighter PNe. The faintest and most evolved PNe typically cluster in areas of colour-colour space occupied by ordinary stars. Possible reasons for the wide disparity in infrared colour-colour ratios, such as evolution and dust composition, are presented for evaluation. A correlation is found between the optical luminosity of PNe, emission-line ratios and the MIR dust luminosity at various bands. Luminosity functions using the four Infrared Array Camera and Multiband Imaging Photometer of Spitzer (MIPS) 24 bands are directly compared, revealing an increasing accumulation of PNe within the brightest two magnitudes at longer wavelengths. A correlation is also found between the MIPS 24 band and the O iii 5007 and Hβ fluxes.
This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were ...identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R ∼ 31,500) with the 3.5 m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from Fe i lines, taking into account non-LTE corrections and using differential abundances with respect to a set of standards. Of the 126 new stars, 124 have Fe/H < −1.5, 105 have Fe/H < −2.0, and 4 have Fe/H < −3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3 ≤ Eu/Fe ≤ +1.0 and Ba/Eu < 0) and 4 new r-II stars (with Eu/Fe > +1.0). Nineteen stars are found to exhibit a "limited-r" signature (Sr/Ba > +0.5, Ba/Eu < 0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, , and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
Our previous identification and spectroscopic confirmation of 431 faint, new planetary nebulae (PNe) in the central 25 deg2 region of the Large Magellanic Cloud (LMC) permit us to now examine the ...shape of the LMC planetary nebula luminosity function (PNLF) through an unprecedented 10 mag range. The majority of our newly discovered and previously known PNe were observed using the 2dF, multi-object fibre spectroscopy system on the 3.9-m Anglo-Australian Telescope and the FLAMES multi-object spectrograph on the 8-m Very Large Telescope. We present reliable O iii 5007 Å and Hβ flux estimates based on calibrations to well-established PN fluxes from previous surveys and spectroscopic standard stars. The bright cut-off (M*) of the PNLF is found by fitting a cumulative function to the bright end of the PNLF over a 3.4 mag range. This cut-off is used to estimate a new distance modulus of 18.46 to the LMC, in close agreement with previous PNLF studies and the best estimates by other indicators. The bright-end cut-off is robust to small samples of bright PNe since significantly increased PN samples do not change this fiducial. We then fit a truncated exponential curve directly to the bright end of the function over a 6 mag range and test the curve's ability to indicate the position of M*. Because of the significant increase in the number of LMC PNe, the shape of the PNLF is now examined in greater detail than has previously been possible. Newly discovered features include a small increase in the number of PNe over the brightest 4 mag followed by a steep rise over 2 mag, a peak at 6 mag below the bright cut-off and an almost linear drop-off to the faint end. Dips at the bright end of the PNLF are examined in relation to the overall shape of the PNLF and the exponential increase in the number of PNe. Through cumulative functions, the new LMC PNLF is compared to those from the Small Magellanic Cloud and a new deep local Galactic sample revealing the effects of incompleteness. The new O iii 5007 Å LMC PNLF is then compared to our new Hβ LMC PNLF using calibrated and measured fluxes for the same objects, revealing the effects of metallicity on the O iii 5007 Å line.
Abstract
This compilation is the fourth data release from the
R
-Process Alliance (RPA) search for
r
-process-enhanced stars and the second release based on “snapshot” high-resolution (
R
∼ 30,000) ...spectra collected with the du Pont 2.5 m Telescope. In this data release, we propose a new delineation between the
r
-I and
r
-II stellar classes at
, instead of the empirically chosen
level previously in use, based on statistical tests of the complete set of RPA data released to date. We also statistically justify the minimum level of Eu/Fe for definition of the
r
-I stars, Eu/Fe > +0.3. Redefining the separation between
r
-I and
r
-II stars will aid in the analysis of the possible progenitors of these two classes of stars and determine whether these signatures arise from separate astrophysical sources at all. Applying this redefinition to previous RPA data, the number of identified
r
-II and
r
-I stars changes to 51 and 121, respectively, from the initial set of data releases published thus far. In this data release, we identify 21 new
r
-II, 111 new
r
-I (plus 3 re-identified), and 7 new (plus 1 re-identified) limited-
r
stars out of a total of 232 target stars, resulting in a total sample of 72 new
r
-II stars, 232 new
r
-I stars, and 42 new limited-
r
stars identified by the RPA to date.
The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia ...Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS ( 200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature Teff, surface gravity log g, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.
This paper reports variations of polycyclic aromatic hydrocarbons (PAHs) features that were found in Spitzer Space Telescope spectra of carbon-rich post-asymptotic giant branch (post-AGB) stars in ...the Large Magellanic Cloud (LMC). The paper consists of two parts. The first part describes our Spitzer spectral observing programme of 24 stars including post-AGB candidates. The latter half of this paper presents the analysis of PAH features in 20 carbon-rich post-AGB stars in the LMC, assembled from the Spitzer archive as well as from our own programme. We found that five post-AGB stars showed a broad feature with a peak at 7.7 μm, that had not been classified before. Further, the 10-13 μm PAH spectra were classified into four classes, one of which has three broad peaks at 11.3, 12.3 and 13.3 μm rather than two distinct sharp peaks at 11.3 and 12.7 μm, as commonly found in H ii regions. Our studies suggest that PAHs are gradually processed while the central stars evolve from post-AGB phase to planetary nebulae, changing their composition before PAHs are incorporated into the interstellar medium. Although some metallicity dependence of PAH spectra exists, the evolutionary state of an object is more significant than its metallicity in determining the spectral characteristics of PAHs for LMC and Galactic post-AGB stars.
Abstract
We present new, accurate positions, spectral classifications, radial and rotational velocities, Hα fluxes, equivalent widths and B, V, I, R magnitudes for 579 hot emission-line stars ...(classes B0-F9) in the Large Magellanic Cloud (LMC) which include 469 new discoveries. Candidate emission-line stars were discovered using a deep, high-resolution Hα map of the central 25 degree2 of the LMC obtained by median stacking a dozen 2 h Hα exposures taken with the UK Schmidt Telescope (UKST). Spectroscopic follow-up observations on the Anglo-Australian Telescope, the UKST, the Very Large Telescope, the South African Astronomical Observatory 1.9 m and the 2.3-m telescope at Siding Spring Observatory have established the identity of these faint sources down to magnitude R
equiv ∼ 23 for Hα (4.5 × 10−17 ergs cm−2 s−1 Å−1).
Confirmed emission-line stars have been assigned an underlying spectral classification through cross-correlation against 131 absorption line template spectra covering the range O1-F8. We confirm 111 previously identified emission-line stars and 64 previously known variable stars with spectral types hotter than F8. The majority of hot stars identified (518 stars or 89 per cent) are of class B. Of all the hot emission-line stars in classes B-F, 130 or 22 per cent are type Be, characterized by the presence of forbidden emission lines such as S ii, N ii and O ii. We report on the physical location of these stars with reference to possible contamination from ambient H ii emission. Only 13 of the emission-line stars require additional high-resolution spectroscopic observations in order to assign a spectroscopic classification. They have nonetheless been added to the catalogue.
Along with flux calibration of the Hα emission, we provide the first Hα luminosity function for selected sub-samples after correction for any possible nebula or ambient contamination. We find a moderate correlation between the intensity of Hα emission and the V magnitude of the central star based on SuperCOSMOS magnitudes and Optical Gravitational Lensing Experiment (OGLE)-II photometry where possible. Cool stars from classes G-S, with and without strong Hα emission, will be the focus of Part II in this series.
We have extended our planetary nebulae (PNe) survey to the outer ∼64 deg2 of the Large Magellanic Cloud (LMC) using maps from the Magellanic Cloud Emission Line Survey (MCELS) and the UK Schmidt ...Telescope (UKST) Hα survey. Although the MCELS survey has poorer ∼5 arcsec resolution than both the UKST Hα survey and the original Hα median stacked map in the LMC's central 25 deg2, it has the advantage of additional narrow-band filters at Hα, O iii and S ii providing improved diagnostic capabilities. Using these data to uncover new emission line candidates we have so far spectroscopically confirmed an extra 63 LMC PNe which we present here for the first time. We have also independently recovered and spectroscopically confirmed 107 of the 109 (98 per cent) PNe that were previously known to exist in the outer LMC. The majority of our newly discovered and previously known PNe were confirmed using the AAOmega, multi-object fibre spectroscopy system on the 3.9-m Anglo-Australian Telescope (AAT) and the 6dF multi-object spectrograph on the UKST. These newly identified PNe were cross-checked against extant multi-wavelength imaging surveys in the near- and mid-infrared in particular and against the latest emission-line ratio diagnostic plots for improved confidence in PNe identification.
The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems ...in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo–three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research.
This paper presents accurate homogeneous positions, velocities and other pertinent properties for 460 newly discovered and 169 previously known planetary nebulae (PNe) in the central 25-deg2 bar ...region of the Large Magellanic Cloud (LMC). Candidate emission sources were discovered using a deep, high-resolution Hα map of the LMC obtained by median stacking a dozen 2 h Hα exposures taken with the UK Schmidt Telescope (UKST). Our spectroscopic follow-up of more than 2000 compact (i.e. <20 arcsec) Hα emission candidates uncovered has tripled the number of PNe in this area. All of the 169 previously known PNe within this region have also been independently recovered and included in this paper to create a homogeneous data set. Of the newly discovered PNe, we classify 291 as ‘true’, 54 as ‘likely’ and 115 as ‘possible’ based on the strength of photometric and spectroscopic evidence. Radial velocities have been measured using both weighted averaging of emission lines and cross-correlation techniques against high-quality templates. Based on the median comparison of the two systems, we define a measurement error of ±4 km s−1. A new velocity map of the central 25 deg2 of the LMC, based on results from the combined new and previously known PNe, is presented, indicating an averaged heliocentric velocity differential of 65 km s−1 perpendicular to the line of nodes for the entire PN population across our survey area. Averaged velocities of our PNe and molecular hydrogen (from the literature) across 37 × 37 arcmin2 subareas are compared. The PNe are found to have a higher vertical velocity dispersion than the H i disc to a maximum of 10 times the spread of the H i disc, in keeping with the findings of Meatheringham et al. In addition, moving out from the main bar, we find that the PN population follows a plane which is somewhat warped in relation to the H i disc. We estimate the total PN population of the entire LMC system, based on our Requiv Hα limiting magnitude of ∼22, to be 956 ± 141.
PDF
