| 1. |
- Aleman, I., et al.
(författare)
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Herschel Planetary Nebula Survey (HerPlaNS) First detection of OH+ in planetary nebulae
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We report the first detections of OH+ emission in planetary nebulae (PNe). Methods. As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the PACS and SPIRE instruments aboard the Herschel Space Observatory, we performed a line survey in these PNe over the entire spectral range between 51 mu m and 672 mu m to look for new detections. Results. The rotational emission lines of OH+ at 152.99, 290.20, 308.48, and 329.77 mu m were detected in the spectra of three planetary nebulae: NGC 6445, NGC6720, and NGC 6781. Excitation temperatures and column densities derived from these lines are in the range of 27-47 K and 2 x 10(10)-4 x 10(11) cm(-2), respectively. Conclusions. In PNe, the OH+ rotational line emission appears to be produced in the photodissociation region (PDR) in these objects. The emission of OH+ is observed only in PNe with hot central stars (T-eff > 100 000 K), suggesting that high-energy photons may play a role in OH+ formation and its line excitation in these objects, as seems to be the case for ultraluminous galaxies.
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| 2. |
- Morabito, L. K., et al.
(författare)
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Discovery of Carbon Radio Recombination Lines in M82
- 2014
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 795:2, s. Art. no. L33-
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Forskningsöversikt (refereegranskat)abstract
- Carbon radio recombination lines (RRLs) at low frequencies (less than or similar to 500 MHz) trace the cold, diffuse phase of the interstellar medium, which is otherwise difficult to observe. We present the detection of carbon RRLs in absorption in M82 with the Low Frequency Array in the frequency range of 48-64 MHz. This is the first extragalactic detection of RRLs from a species other than hydrogen, and below 1 GHz. Since the carbon RRLs are not detected individually, we cross-correlated the observed spectrum with a template spectrum of carbon RRLs to determine a radial velocity of 219 km s(-1). Using this radial velocity, we stack 22 carbon-alpha transitions from quantum levels n = 468-508 to achieve an 8.5 sigma detection. The absorption line profile exhibits a narrow feature with peak optical depth of 3x10(-3) and FWHM of 31 km s(-1). Closer inspection suggests that the narrow feature is superimposed on a broad, shallow component. The total line profile appears to be correlated with the 21 cm Hi line profile reconstructed from Hi absorption in the direction of supernova remnants in the nucleus. The narrow width and centroid velocity of the feature suggests that it is associated with the nuclear starburst region. It is therefore likely that the carbon RRLs are associated with cold atomic gas in the direction of the nucleus of M82.
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| 3. |
- Ueta, T., et al.
(författare)
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Herschel Planetary Nebula Survey (HerPlaNS)
- 2014
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Ingår i: Asymmetrical Planetary Nebulae VI conference, Proceedings of the conference held 4-8 November, 2013. ; , s. 106-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Herschel Planetary Nebula Survey (HerPlaNS) is one of the largest Open Time programs carried out by the Herschel Space Observatory, by which we simultaneously probe the dust and gas components of the circumstellar environments of evolved stars. HerPlaNS is part of a community-wide panchromatic (from X-ray to Radio) observational initiative to furnish substantial PN data resources that would allow us - PN astronomers - to tackle a multitude of issues in PN physics. In this contribution we will give a general overview of the survey and a glimpse of what the data can tell us using NGC 6781 as an example.
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