skip to main content

Explore Research Products in the NSF-PAR

Title: Carbon Isotope Ratios in Planetary Nebulae: The Unexpected Enhancement of 13C
The 12C/13C ratio has been measured toward a sample of planetary nebulae (PNe) using millimeter observations of CO, HCN, HNC, CN, and other species, conducted with the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory. The observed nebulae spanned the entire lifetime of PNe, from ∼900 to 12,000 yr, and include well-known objects such as NGC 7293 (Helix), NGC 6720 (Ring), and NGC 2440, as well as relatively unexplored nebulae (M3–28, M2–48, and M3–55). In most cases, multiple molecules and transitions were used in the ratio determination, resulting in the most accurate values available to date, with 10%–40% uncertainties. The ratios found were unexpectedly low, lying in the range 12C/13C ∼1.0 ± 0.7–13.2 ± 4.9, with an average value of 3.7—drastically less than found in the envelopes of C-rich AGB stars, and, in some cases, lower than the minimum value achieved in equilibrium CNO burning. Such low values are expected for the two O-rich nebulae studied (M2–9 and M2–48), because of insufficient third dredge-up events. However, most of the PNe observed were clearly carbon-rich, as deduced from the large number of C-bearing molecules present in them. Because nucleosynthesis ceases in the PN stage, both the C/O and the 12C/13C ratios must reflect abundances at the end of the AGB. These consistently low 12C/13C ratios, combined with the bipolar/multipolar morphologies of all planetary nebulae observed, suggest an explosive process involving proton-capture occurred at the AGB–PN transition.  more » « less
Award ID(s):
1907910
NSF-PAR ID:
10203352
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
The astrophysical journal
Volume:
900
ISSN:
2041-8205
Page Range / eLocation ID:
L31
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al ( , Science)

    Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe.

     
    more » « less
  2. ; ; ; ; ; ; ; ( , Astronomy & Astrophysics)

    Aims.We perform a deep survey of planetary nebulae (PNe) in the spiral galaxy NGC 300 to construct its planetary nebula luminosity function (PNLF). We aim to derive the distance using the PNLF and to probe the characteristics of the most luminous PNe.

    Methods.We analysed 44 fields observed with MUSE at the VLT, covering a total area of ∼11 kpc2. We find [O III]λ5007 sources using the differential emission line filter (DELF) technique. We identified PNe through spectral classification with the aid of the BPT diagram. The PNLF distance was derived using the maximum likelihood estimation technique. For the more luminous PNe, we also measured their extinction using the Balmer decrement. We estimated the luminosity and effective temperature of the central stars of the luminous PNe based on estimates of the excitation class and the assumption of optically thick nebulae.

    Results.We identify 107 PNe and derive a most-likely distance modulus $ (m-M)_0 = 26.48^{+0.11}_{-0.26} $ ($ d = 1.98^{+0.10}_{-0.23} $ Mpc). We find that the PNe at the PNLF cutoff exhibit relatively low extinction, with some high-extinction cases caused by local dust lanes. We present the lower limit luminosities and effective temperatures of the central stars for some of the brighter PNe. We also identify a few Type I PNe that come from a young population with progenitor masses > 2.5 M⊙but do not populate the PNLF cutoff.

    Conclusions.The spatial resolution and spectral information of MUSE allow precise PN classification and photometry. These capabilities also enable us to resolve possible contamination by diffuse gas and dust, improving the accuracy of the PNLF distance to NGC 300.

     
    more » « less
  3. ; ; ; ; ; ; ( , Monthly Notices of the Royal Astronomical Society)
    ABSTRACT

    Theory predicts that the temperature of the X-ray-emitting gas (∼106 K) detected from planetary nebulae (PNe) is a consequence of mixing or thermal conduction when in contact with the ionized outer rim (∼104 K). Gas at intermediate temperatures (∼105 K) can be used to study the physics of the production of X-ray-emitting gas, via C iv, N v, and O vi ions. Here, we model the stellar atmosphere of the CSPN of NGC 1501 to demonstrate that even this hot H-deficient [WO4]-type star cannot produce these emission lines by photoionization. We use the detection of the C iv lines to assess the physical properties of the mixing region in this PNe in comparison with its X-ray-emitting gas, rendering NGC 1501 only the second PNe with such characterization. We extend our predictions to the hottest [WO1] and cooler [WC5] spectral types and demonstrate that most energetic photons are absorbed in the dense winds of [WR] CSPN and highly ionized species can be used to study the physics behind the production of hot bubbles in PNe. We found that the UV observations of NGC 2452, NGC 6751, and NGC 6905 are consistent with the presence mixing layers and hot bubbles, providing excellent candidates for future X-ray observations.

     
    more » « less
  4. ; ; ; ; ( , The Astrophysical Journal)
    Abstract Observations of HCN and HCO + have been carried out toward 13 planetary nebulae (PNe) using the facilities of the Arizona Radio Observatory (ARO). These nebulae represent a wide range of morphologies and ages (∼2000–28,000 yr). For both molecules, the J = 1 → 0 transitions at 88–89 GHz and the J = 3 → 2 lines at 265–267 GHz were measured, together with CO lines ( J = 1 → 0, 2 → 1, and 3 → 2, depending on the source), using the ARO 12 m and Submillimeter Telescopes. HCN and HCO + were detected with at least one transition in 10 nebulae: He 2-459, Hu 1-1, K3-52, K3-65, M1-8, M1-40, M1-59, M2-53, M4-17, and NGC 6445. HCO + was additionally identified via two transitions in Na 2. Some observed line profiles were complex, with multiple velocity components tracing varied outflows. From radiative transfer modeling, column densities were established for HCN and HCO + : N tot (HCN) = 0.005–1.1 × 10 14 and N tot (HCO + ) = 0.008–9.5 × 10 13 cm −2 . Gas densities of n (H 2 ) ∼ 10 5 –10 7 cm −3 were also determined for all PNe. Fractional abundances with respect to H 2 , calculated using CO as a proxy, are f (HCN) ∼ 0.2–1.5 × 10 −7 and f (HCO + ) ∼ 0.3–5.1 × 10 −8 . The abundances of HCN and HCO + did not significantly vary with nebular age to 28,000 yr. Combined with previous observations, at least 30 PNe contain HCN and/or HCO + , indicating that polyatomic molecules are common constituents of these objects. The data strongly support a scenario where dense ejecta from PNe seed the interstellar medium with molecular material. 
    more » « less
  5. ; ; ; ; ; ; ( , Monthly Notices of the Royal Astronomical Society)
    ABSTRACT

    Open clusters are relatively young and numerous. These systems are distributed throughout the Galactic disc and provide insights on the chemistry of the Milky Way. In this study, we provide a near-infrared spectroscopic analysis of four stars of the young open cluster NGC 2345. Our infrared data present a resolving power of R ≈ 45 000, covering the H- and K-bands (1.5–2.5 μm), and high-signal-to-noise ratio, which are gathered with the Immersion Grating Infrared Spectrograph (IGRINS) at the Gemini Observatory. From atmospheric parameters previously derived via optical spectroscopy, we obtain abundances for C (12C16O), N (12C14N), O (16OH), F (H19F), Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, Cr, Fe, Ni, Ce, Nd, and Yb. Additionally, the 12C/13C (13C16O), 16O/17O (12C17O), and 16O/18O (12C18O) isotopic ratios are obtained. We compare the infrared results with a previous work based on optical spectral analysis, but chemical species such as F, S, P, K, and Yb are determined for the first time in stars of NGC 2345. We also confirm a low metallicity ([Fe/H]  =  −0.32 ± 0.04) and slight enrichment in s-process elements, as already noticed in works available in the literature, but we do not find any enrichment in F. Our results demonstrate excellent agreement between our measured isotopic ratios 12C/13C and 16C/17O and models of stellar nucleosynthesis, while we find that the abundance of 18O is overestimated in comparison to our measurements. Finally, we assess our findings in comparison to the chemical patterns observed in open clusters, classified by both their age and Galactocentric distances, and highlight the need for a more comprehensive sample of young clusters within the 9–11 kpc range for a proper comparison.

     
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email