Spectroscopic survey of faint planetary-nebula nuclei. II. The subdwarf O central star of Fr 2-30
arXiv:2305.16247 · doi:10.1093/mnras/stad1624
Abstract
Fr 2-30 = PN? G126.8-15.5 is a faint emission nebula, hosting a 14th-mag central star that we identify here for the first time. Deep Halpha and [O III] images reveal a roughly elliptical nebula with dimensions of at least 22'x14', fading into a surrounding network of even fainter emission. Optical spectrograms of the central star show it to have a subdwarf O spectral type, with a Gaia parallax distance of 890 pc. A model-atmosphere analysis gives parameters of Teff = 60,000 K, log g = 6.0, and a low helium content of nHe/nH = 0.0017. The location of the central star in the log g -- Teff plane is inconsistent with a post-asymptotic-giant-branch evolutionary status. Two alternatives are that it is a helium-burning post-extreme-horizontal-branch object, or a hydrogen-burning post-red-giant-branch star. In either case the evolutionary ages are so long that a detectable planetary nebula (PN) should not be present. We find evidence for a variable radial velocity (RV), suggesting that the star is a close binary. However, there are no photometric variations, and the spectral-energy distribution rules out a companion earlier than M2 V. The RVs of the star and surrounding nebula are discordant, and the nebula lacks typical PN morphology. We suggest that Fr 2-30 is a "PN mimic" -- the result of a chance encounter between the hot sdO star and an interstellar cloud. However, we note the puzzling fact that there are several nuclei of genuine PNe that are known to be in evolutionary states similar to that of the Fr 2-30 central star.
arXiv commentAccepted by MNRAS
References in corpus (27)
- The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
- The Gaia mission
- The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
- The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
- The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)
- The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
- Ultraviolet Radiation from Evolved Stellar Populations -- I. Models
- Hot subluminous stars
- Three-dimensional mapping of the local interstellar medium with composite data
- Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs
- Planetary Nebulae: Observational Properties, Mimics, and Diagnostics
- The HETDEX Instrumentation: Hobby-Eberly Telescope Wide Field Upgrade and VIRUS
- HASH: the Hong Kong/AAO/Strasbourg H-alpha planetary nebula database
- The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars
- Population of hot subdwarf stars studied with Gaia III. Catalogue of known hot subdwarf stars: Data Release 2
- High-resolution FUSE and HST ultraviolet spectroscopy of the white dwarf central star of Sh 2-216
- Planetary nebulae after common-envelope phases initiated by low-mass red giants
- PHL 932: when is a planetary nebula not a planetary nebula?
- Hot subdwarf stars identified in Gaia DR2 with spectra of LAMOST DR6 and DR7 I. Single-lined spectra
- Binaries discovered by the SPY survey VI. Discovery of a low mass companion to the hot subluminous planetary nebula central star EGB\,5 - A recently ejected common envelope?
- Hot Subdwarf Stars Identified in Gaia DR2 with Spectra of LAMOST DR6 and DR7. II. Kinematics
- Hunting for Extremely Faint Planetary Nebulae in the SDSS Spectroscopic Database
- The post-common-envelope binary central star of the planetary nebula Ou 5: a doubly-eclipsing post-red-giant-branch system
- Spectral analysis of four surprisingly similar hot hydrogen-rich subdwarf O stars
- Spectroscopic survey of faint planetary-nebula nuclei. I. Six new "O VI" central stars
- Hot white dwarfs and pre-white dwarfs discovered with SALT
- Post-red-giant-branch Planetary Nebulae