Hoadley, Keri and Martin, D. Christopher and Metzger, Brian D. and Seibert, Mark and McWilliam, Andrew and Shen, Ken J. and Neill, James D. and Stefansson, Gudmundur and Monson, Andrew and Schaefer, Bradley E. (2020) A blue ring nebula from a stellar merger several thousand years ago. Nature, 587 (7834). pp. 387-391. ISSN 0028-0836. doi:10.1038/s41586-020-2893-5. https://resolver.caltech.edu/CaltechAUTHORS:20200810-151015540
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Abstract
Stellar mergers are a brief but common phase in the evolution of binary star systems. These events have many astrophysical implications; for example, they may lead to the creation of atypical stars (such as magnetic stars, blue stragglers and rapid rotators), they play an important part in our interpretation of stellar populations and they represent formation channels of compact-object mergers. Although a handful of stellar mergers have been observed directly, the central remnants of these events were shrouded by an opaque shell of dust and molecules, making it impossible to observe their final state (for example, as a single merged star or a tighter, surviving binary). Here we report observations of an unusual, ring-shaped ultraviolet (‘blue’) nebula and the star at its centre, TYC 2597-735-1. The nebula has two opposing fronts, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the Galactic plane suggest that it is an old star, yet it has abnormally low surface gravity and a detectable long-term luminosity decay, which is uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission—signatures of dusty circumstellar disks, stellar activity and accretion. Combined with stellar evolution models, the observations suggest that TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, enabling the direct study of the merging process.
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| Alternate Title: | A "blue ring nebula" surrounding a thousands of years old stellar merger | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Additional Information: | © 2020 Springer Nature. Received 04 May 2020. Accepted 01 September 2020. Published 18 November 2020. This research is based on observations made with GALEX, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5–26555. Some of the data presented were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California and NASA. This research made use of the Keck Observatory Archive, which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute, under contract with NASA, and made possible by the financial support of the W. M. Keck Foundation. We recognize and acknowledge the very important cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are fortunate to have the opportunity to conduct observations from this mountain. Some of the data presented were obtained at the Palomar Observatory. This research made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We thank V. Scowcroft for obtaining Spitzer/IRAC photometry of TYC 2597-735-1. Funding for APASS was provided by the Robert Martin Ayers Sciences Fund. The DASCH data from the Harvard archival plates was partially supported from National Science Foundation (NSF) grants AST-0407380, AST-0909073 and AST-1313370. The American Association of Variable Star Observers has been helpful for finder charts, comparison star magnitudes and recruiting skilled observers, including S. Dufoer, K. Menzies, R. Sabo, G. Stone, R. Tomlin and G. Walker. These results are based on observations obtained with the HPF on the Hobby–Eberly Telescope (HET), which is named in honour of its principal benefactors, William P. Hobby and Robert E. Eberly. These data were obtained during HPF’s engineering and commissioning period. We thank the resident astronomers and telescope operators at the HET for the execution of our observations with HPF. We thank C. Cañas for providing an independent verification of the HPF SERVAL pipeline using a CCF-based method to calculate the radial velocities, which resulted in fully consistent radial velocities to the SERVAL-based radial velocities presented here. The HET is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München and Georg-August Universität Gottingen. The HET collaboration acknowledges support and resources from the Texas Advanced Computing Center. This work was partially supported by funding from the Center for Exoplanets and Habitable Worlds, which is supported by the Pennsylvania State University, the Eberly College of Science and the Pennsylvania Space Grant Consortium. We thank A. Gil de Paz for obtaining the narrow-band-filter Hα imagery, J. Johnson for commissioning TYC 2597-735-1 radial velocity measurements as part of the California Planet Finder programme, and A. Howard for leading Keck–HIRES spectra and performing the primary radial-velocity reduction on all HIRES data. K.H. acknowledges support from a David and Ellen Lee Postdoctoral Fellowship in Experimental Physics at Caltech, and thanks L. Hillenbrand and E. Hamden for discussions about aspects of this work. B.D.M. acknowledges support from the Hubble Space Telescope (number HST-AR-15041.001-A) and the NSF (number 80NSSC18K1708). K.J.S. received support from the NASA Astrophysics Theory Program (NNX17AG28G). G.S. and A.Mo. acknowledge support from NSF grants AST-1006676, AST-1126413, AST-1310885, AST-1517592, AST-1310875 and AST-1907622, the NASA Astrobiology Institute (NNA09DA76A) and PSARC in their pursuit of precision radial velocities in the near-infrared with HPF. We acknowledge support from the Heising-Simons Foundation via grant 2017-0494 and 2019-1177. Computations for this research were performed on the Pennsylvania State University’s Institute for Computational and Data Sciences. G.S. acknowledges support by NASA HQ under the NASA Earth and Space Science Fellowship Program through grant NNX16AO28H, and is a Henry Norris Russell Fellow. Data availability: All GALEX imaging and grism data of TYC 2597-735-1 and its ultraviolet nebula are publicly available from the Mikulski Archive for Space Telescopes (MAST) in raw and reduced formats (http://galex.stsci.edu/GalexView/ or https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html). All Keck–LRIS and Keck–HIRES data for TYC 2597-735-1 are publicly available from the Keck Observatory Archive (https://koa.ipac.caltech.edu/cgi-bin/KOA/nph-KOAlogin). TYC 2597-735-1 raw photometric light-curve frames, plates and light curves from 1895 to 1985 are publicly available as a part of the DASCH programme (https://projects.iq.harvard.edu/dasch). Data for the more recent photmetry for the light-curve construction is available from the corresponding author on request. All other photometric data for TYC 2597-735-1 were obtained from publicly archived ground- and space-based imaging and surveys, stored on the SIMBAD Astronomical Database (http://simbad.u-strasbg.fr/simbad/) and the NASA/IPAC Infrared Science Archive (https://irsa.ipac.caltech.edu/frontpage/). The relevant data products from the Habitable-zone Planet Finder Spectrograph (HPF) campaign for TYC 2597-735-1 are publicly available at https://github.com/oglebee-chessqueen/BlueRingNebula.git. Code availability. We used MESA for a portion of our analysis. Although MESA is readily available for public use, we used a custom subroutine and MESA inline code to produce the TYC 2597-735-1 merger evolution model, publicly available at https://github.com/oglebee-chessqueen/BlueRingNebula.git. Use the ATLAS9 pre-set grid of synthetic stellar spectra to fit the TYC 2597-735-1 spectral energy distribution to representative stellar spectra. All synthetic stellar spectra are publicly available at https://www.stsci.edu/hst/instrumentation/reference-data-for-calibration-and-tools/astronomical-catalogues/castelli-and-kurucz-atlas. Portions of our analysis used community-developed core Python packages for astronomy, photutils and astropy. These authors contributed equally: Keri Hoadley, D. Christopher Martin, Brian D. Metzger, Mark Seibert. Author Contributions. K.H. and B.D.M. organized and wrote the main body of the paper. K.H. and M.S. performed the data reduction and analysis of the GALEX data, investigated the source of the ultraviolet emission, quantified the mass the far-ultraviolet nebula, and led the the analysis of the Hα emission and variability of TYC 2597-735-1. B.D.M. led all theoretical and analytic interpretation efforts of the ultraviolet nebula origins and TYC 2597-735-1 in the context of stellar mergers and present-day luminous red novae. D.C.M. and M.S. led the GALEX programme that led to the detection of the ultraviolet nebula in 2004 and all subsequent follow-up observations of the nebula with GALEX; both contributed to the overall interpretation of the observational data. D.C.M. contributed to the organization and writing of the paper. M.S. led the radial-velocity analysis and the interpretation and analysis of the infrared excess in the spectral energy distribution of TYC 2597-735-1, modelled this distribution (stellar and dust infrared excess components), and coordinated all ground-based observations of the blue ring nebula and TYC 2597-735-1 at Palomar Observatory and W. M. Keck Observatory. K.H. also helped in the interpretation and analysis of the infrared excess in the spectral energy distribution of TYC 2597-735-1. A.Mc. derived the physical parameters, performed the model atmosphere chemical abundance analysis of TYC 2597-735-1, and participated in discussions of observations, analysis and interpretation. K.J.S. performed the MESA calculations and participated in discussions of observations, analysis and interpretation. J.D.N. handled the data analysis, reported the result of the velocity structure of the Hα shock observed with Keck–LRIS, and participated in discussions of observations, analysis and interpretation. G.S. performed the HET–HPF radial-velocity and differential line-width indicator extractions and provided expertise on the interpretation of the combined radial-velocity datasets. A.Mo. coordinated HET–HPF observations, and performed and reduced all TMMT B-band observations. B.E.S. extracted and analysed the long-term light-curve data from May 1897 to September 2019. The authors declare no competing interests. Peer review information. Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Group: | Astronomy Department, Space Astrophysics Laboratory | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Subject Keywords: | Stars; Stellar evolution | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Issue or Number: | 7834 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| DOI: | 10.1038/s41586-020-2893-5 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Record Number: | CaltechAUTHORS:20200810-151015540 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20200810-151015540 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Official Citation: | Hoadley, K., Martin, D.C., Metzger, B.D. et al. A blue ring nebula from a stellar merger several thousand years ago. Nature 587, 387–391 (2020). https://doi.org/10.1038/s41586-020-2893-5 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ID Code: | 104897 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Collection: | CaltechAUTHORS | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Deposited By: | George Porter | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Deposited On: | 18 Nov 2020 17:01 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Last Modified: | 16 Nov 2021 18:37 |
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