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Optically visible post-AGB/RGB stars and young stellar objects in the small magellanic cloud: Candidate selection, spectral energy distributions and spectroscopic examination

Kamath, Devika; van Winckel, Hans; Wood, Peter R

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We have carried out a search for optically visible post-asymptotic giant branch (post-AGB) candidates in the Small Magellanic Cloud (SMC). First, we used mid-IR observations from the Spitzer Space Telescope to select optically visible candidates with excess mid-IR flux and then we obtained low-resolution optical spectra for 801 of the candidates. After removing poorquality spectra and contaminants, such as M-stars, C-stars, planetary nebulae, quasi-stellar objects and background galaxies, we...[Show more]

dc.contributor.authorKamath, Devika
dc.contributor.authorvan Winckel, Hans
dc.contributor.authorWood, Peter R
dc.date.accessioned2015-12-10T23:34:20Z
dc.identifier.issn0035-8711
dc.identifier.urihttp://hdl.handle.net/1885/69399
dc.description.abstractWe have carried out a search for optically visible post-asymptotic giant branch (post-AGB) candidates in the Small Magellanic Cloud (SMC). First, we used mid-IR observations from the Spitzer Space Telescope to select optically visible candidates with excess mid-IR flux and then we obtained low-resolution optical spectra for 801 of the candidates. After removing poorquality spectra and contaminants, such as M-stars, C-stars, planetary nebulae, quasi-stellar objects and background galaxies, we ended up with a final sample of 63 high-probability post-AGB/RGB candidates of A-F spectral type. From the spectral observations, we estimated the stellar parameters: effective temperature (Teff), surface gravity (log g) and metallicity ([Fe/H]). We also estimated the reddening and deduced the luminosity using the stellar parameters combined with photometry. For the post-AGB/RGB candidates, we found that the metallicity distribution peaks at [Fe/H] =-1.00 dex. Based on a luminosity criterion, 42 of these 63 sources were classified as post-red giant branch (post-RGB) candidates and the remaining 21 as post-AGB candidates. From the spectral energy distributions, we were able to infer that 6 of the 63 post-AGB/RGB candidates have a surrounding circumstellar shell suggesting that they are single stars, while 27 of the post-AGB/RGB candidates have a surrounding disc, suggesting that they lie in binary systems. For the remaining 30 post-AGB/RGB candidates the nature of the circumstellar environment was unclear. Variability is displayed by 38 of the 63 post-AGB/RGB candidates with the most common variability types being the Population II Cepheids (including RV-Tauri stars) and semiregular variables. This study has also revealed a new RV Tauri star in the SMC, J005107.19-734133.3, which shows signs of s-process enrichment. From the numbers of post-AGB/RGB stars in the SMC, we were able to estimate evolutionary rates. We find that the number of post-AGB and post-RGB candidates that we have identified are in good agreement with the stellar evolution models with some mass-loss in the post-AGB phase and a small amount of re-accretion in the lower luminosity post-RGB phase. This study also resulted in a new sample of 40 young stellar objects (YSOs) of A-F spectral type. The 40 YSO candidates for which we could estimate stellar parameters are luminous and of high mass (̃3-10Ṁ). They lie on the cool side of the usually adopted birthline in the HR-diagram. This line separates visually obscured protostars from optically visible pre-main-sequence stars, meaning that our YSO candidates have become optically visible in the region of the HR diagram usually reserved for obscured protostars. Additionally, we also identified a group of 63 objects whose spectra are dominated by emission lines and in some cases, a significant UV continuum. These objects are very likely to be either hot post-AGB/RGB candidates or luminous YSOs.
dc.publisherBlackwell Publishing Ltd
dc.sourceMonthly Notices of the Royal Astronomical Society
dc.titleOptically visible post-AGB/RGB stars and young stellar objects in the small magellanic cloud: Candidate selection, spectral energy distributions and spectroscopic examination
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume439
dc.date.issued2014
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationU3488905xPUB2011
local.type.statusPublished Version
local.contributor.affiliationKamath, Devika, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationvan Winckel, Hans, Instituut voor Sterrenkunde
local.contributor.affiliationWood, Peter R, College of Physical and Mathematical Sciences, ANU
local.description.embargo2037-12-31
local.bibliographicCitation.issue3
local.bibliographicCitation.startpage2211
local.bibliographicCitation.lastpage2270
local.identifier.doi10.1093/mnras/stt2033
dc.date.updated2015-12-10T11:32:31Z
local.identifier.scopusID2-s2.0-84896476474
CollectionsANU Research Publications

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