J/ApJ/923/100ivo://CDS.VizieR/J/ApJ/923/100doi:10.26093/cds/vizier.19230100CDSMetzger B.D.Zenati Y.Chomiuk L.Shen K.J.Strader J.2023-09-27T13:35:00Z2023-07-19T15:32:23ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frnovaevisible-astronomyspectroscopyWe explore the observational appearance of the merger of a low-mass star with a white dwarf (WD) binary companion. We are motivated by recent work finding that multiple tensions between the observed properties of cataclysmic variables (CVs) and standard evolution models are resolved if a large fraction of CV binaries merge as a result of unstable mass transfer. Tidal disruption of the secondary forms a geometrically thick disk around the WD, which subsequently accretes at highly super-Eddington rates. Analytic estimates and numerical hydrodynamical simulations reveal that outflows from the accretion flow unbind a large fraction >~90% of the secondary at velocities ~500-1000km/s within days of the merger. Hydrogen recombination in the expanding ejecta powers optical transient emission lasting about a month with a luminosity >~10^38^erg/s, similar to slow classical novae and luminous red novae from ordinary stellar mergers. Over longer timescales the mass accreted by the WD undergoes hydrogen shell burning, inflating the remnant into a giant of luminosity ~300-5000L_{sun}_, effective temperature T_eff_~3000K, and lifetime ~10^4^-10^5^yr. We predict that ~10^3^-10^4^ Milky Way giants are CV merger products, potentially distinguishable by atypical surface abundances. We explore whether any Galactic historical slow classical novae are masquerading CV mergers by identifying four such post-nova systems with potential giant counterparts for which a CV merger origin cannot be ruled out. We address whether the historical transient CK Vul and its gaseous/dusty nebula resulted from a CV merger.2021ApJ...923..100Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/923/100CatalogResearchIsServedByTAP VizieR generic servicerelated-toB/cb : Cataclysmic Binaries, LMXBs, and related objects (Ritter+, 2004)V/110 : Catalog of Cataclysmic Variables (Downes+ 2001)V/123 : Catalog of Cataclysmic Variables (Downes+ 2001-2006)J/A+A/513/L7 : Post common envelope bin. from SDSS. VIII (Schreiber+, 2010)J/ApJ/723/1072 : The ELM survey. I. Low-mass white dwarfs (Brown+, 2010)J/ApJ/730/67 : Radial velocities of low-mass white dwarfs (Brown+, 2011)J/ApJS/194/28 : The evolution of cataclysmic variables (Knigge+, 2011)J/ApJS/197/31 : Swift X-ray obs. of classical novae. II. (Schwarz+, 2011)J/ApJ/788/164 : Known Galactic classical novae (Pagnotta+, 2014)J/ApJ/834/196 : Galactic novae with m<=10 from 1900 to 2015 (Shafter, 2017)J/other/NatAs/2.778 : Hyperfine rot. transitions of 26Al19F (Kaminski+ 2018)J/A+A/630/A75 : Six luminous red novae photometry (Pastorello+, 2019)J/ApJ/910/134 : Swift-XRT light curves of 13 Galactic novae (Gordon+, 2021)J/A+A/653/A134 : AT 2018bwo light curves (Blagorodnova+, 2021)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/923/100https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/923/100http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/923/100https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/923/100https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/923/100http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/923/100GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/ApJ/923/100/fig7The 4.1m Southern Astrophysical Research (SOAR) telescope spectrum of V5558 SgrrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambda[3999.7/7911.8] Wavelength; Angstroms0.1nmem.wldoubleFlux[1.5e-15/1.8e-14] Reduced flux (1)cW.m**-1.nm**-1phot.fluxdoubleRaw[1.5e-15/1.8e-14] Raw flux (1)cW.m**-1.nm**-1phot.fluxdoubleBkgrd[1.8e-16/1.2e-15] Background flux (1)cW.m**-1.nm**-1phot.flux;instr.backgrounddoublee_Flux[1.5e-17/7.4e-17] Uncertainty in Flux (1)cW.m**-1.nm**-1stat.error;phot.fluxdouble