Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability
Autor(a) principal: | |
---|---|
Data de Publicação: | 2021 |
Outros Autores: | , , , , |
Tipo de documento: | Artigo |
Idioma: | eng |
Título da fonte: | Repositório Institucional da UFRGS |
Texto Completo: | http://hdl.handle.net/10183/237173 |
Resumo: | Context. About 10% of all stars exhibit absorption lines of ultra-highly excited (UHE) metals (e.g., O viii) in their optical spectra when entering the white dwarf cooling sequence. This is something that has never been observed in any other astrophysical object, and poses a decades-long mystery in our understanding of the late stages of stellar evolution. The recent discovery of a UHE white dwarf that is both spectroscopically and photometrically variable led to the speculation that the UHE lines might be created in a shock-heated circumstellar magnetosphere. Aims. We aim to gain a better understanding of these mysterious objects by studying the photometric variability of the whole popula tion of UHE white dwarfs, and white dwarfs showing only the He ii line problem, as both phenomena are believed to be connected. Methods. We investigate (multi-band) light curves from several ground- and space-based surveys of all 16 currently known UHE white dwarfs (including one newly discovered) and eight white dwarfs that show only the He ii line problem. Results. We find that 75+8 −13% of the UHE white dwarfs, and 75+9 −19% of the He ii line problem white dwarfs are significantly photo metrically variable, with periods ranging from 0.22 d to 2.93 d and amplitudes from a few tenths to a few hundredths of a magnitude. The high variability rate is in stark contrast to the variability rate amongst normal hot white dwarfs (we find 9+4 −2%), marking UHE and He ii line problem white dwarfs as a new class of variable stars. The period distribution of our sample agrees with both the orbital period distribution of post-common-envelope binaries and the rotational period distribution of magnetic white dwarfs if we assume that the objects in our sample will spin-up as a consequence of further contraction. Conclusions. We find further evidence that UHE and He ii line problem white dwarfs are indeed related, as concluded from their overlap in the Gaia HRD, similar photometric variability rates, light-curve shapes and amplitudes, and period distributions. The lack of increasing photometric amplitudes towards longer wavelengths, as well as the nondetection of optical emission lines arising from the highly irradiated face of a hypothetical secondary in the optical spectra of our stars, makes it seem unlikely that an irradiated late-type companion is the origin of the photometric variability. Instead, we believe that spots on the surfaces of these stars and/or geometrical effects of circumstellar material might be responsible. |
id |
UFRGS-2_a53f2695a913dd6dce3475e4e84f7b17 |
---|---|
oai_identifier_str |
oai:www.lume.ufrgs.br:10183/237173 |
network_acronym_str |
UFRGS-2 |
network_name_str |
Repositório Institucional da UFRGS |
repository_id_str |
|
spelling |
Reindl, NicoleSchaffenroth, VeronikaFiliz, SemihGeier, StephanPelisoli, Ingrid DomingosKepler, Souza Oliveira2022-04-13T04:51:47Z20210004-6361http://hdl.handle.net/10183/237173001139574Context. About 10% of all stars exhibit absorption lines of ultra-highly excited (UHE) metals (e.g., O viii) in their optical spectra when entering the white dwarf cooling sequence. This is something that has never been observed in any other astrophysical object, and poses a decades-long mystery in our understanding of the late stages of stellar evolution. The recent discovery of a UHE white dwarf that is both spectroscopically and photometrically variable led to the speculation that the UHE lines might be created in a shock-heated circumstellar magnetosphere. Aims. We aim to gain a better understanding of these mysterious objects by studying the photometric variability of the whole popula tion of UHE white dwarfs, and white dwarfs showing only the He ii line problem, as both phenomena are believed to be connected. Methods. We investigate (multi-band) light curves from several ground- and space-based surveys of all 16 currently known UHE white dwarfs (including one newly discovered) and eight white dwarfs that show only the He ii line problem. Results. We find that 75+8 −13% of the UHE white dwarfs, and 75+9 −19% of the He ii line problem white dwarfs are significantly photo metrically variable, with periods ranging from 0.22 d to 2.93 d and amplitudes from a few tenths to a few hundredths of a magnitude. The high variability rate is in stark contrast to the variability rate amongst normal hot white dwarfs (we find 9+4 −2%), marking UHE and He ii line problem white dwarfs as a new class of variable stars. The period distribution of our sample agrees with both the orbital period distribution of post-common-envelope binaries and the rotational period distribution of magnetic white dwarfs if we assume that the objects in our sample will spin-up as a consequence of further contraction. Conclusions. We find further evidence that UHE and He ii line problem white dwarfs are indeed related, as concluded from their overlap in the Gaia HRD, similar photometric variability rates, light-curve shapes and amplitudes, and period distributions. The lack of increasing photometric amplitudes towards longer wavelengths, as well as the nondetection of optical emission lines arising from the highly irradiated face of a hypothetical secondary in the optical spectra of our stars, makes it seem unlikely that an irradiated late-type companion is the origin of the photometric variability. Instead, we believe that spots on the surfaces of these stars and/or geometrical effects of circumstellar material might be responsible.application/pdfengAstronomy and astrophysics. Les Ulis. Vol. 647 (Apr. 2021), A184, 22 p.Anãs brancasFotometria astronômicaWhite dwarfsStars : Variables : GeneralStarspotsBinaries : CloseMysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variabilityEstrangeiroinfo:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/openAccessreponame:Repositório Institucional da UFRGSinstname:Universidade Federal do Rio Grande do Sul (UFRGS)instacron:UFRGSTEXT001139574.pdf.txt001139574.pdf.txtExtracted Texttext/plain109819http://www.lume.ufrgs.br/bitstream/10183/237173/2/001139574.pdf.txtf3191a62405447308ed366f8bd629565MD52ORIGINAL001139574.pdfTexto completo (inglês)application/pdf5723375http://www.lume.ufrgs.br/bitstream/10183/237173/1/001139574.pdf2cf672d7081d4434be872e41df0d0c13MD5110183/2371732022-04-20 04:53:16.53683oai:www.lume.ufrgs.br:10183/237173Repositório de PublicaçõesPUBhttps://lume.ufrgs.br/oai/requestopendoar:2022-04-20T07:53:16Repositório Institucional da UFRGS - Universidade Federal do Rio Grande do Sul (UFRGS)false |
dc.title.pt_BR.fl_str_mv |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
title |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
spellingShingle |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability Reindl, Nicole Anãs brancas Fotometria astronômica White dwarfs Stars : Variables : General Starspots Binaries : Close |
title_short |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
title_full |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
title_fullStr |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
title_full_unstemmed |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
title_sort |
Mysterious, variable, and extremely hot : white dwarfs showing ultra-high excitation lines : I. Photometric variability |
author |
Reindl, Nicole |
author_facet |
Reindl, Nicole Schaffenroth, Veronika Filiz, Semih Geier, Stephan Pelisoli, Ingrid Domingos Kepler, Souza Oliveira |
author_role |
author |
author2 |
Schaffenroth, Veronika Filiz, Semih Geier, Stephan Pelisoli, Ingrid Domingos Kepler, Souza Oliveira |
author2_role |
author author author author author |
dc.contributor.author.fl_str_mv |
Reindl, Nicole Schaffenroth, Veronika Filiz, Semih Geier, Stephan Pelisoli, Ingrid Domingos Kepler, Souza Oliveira |
dc.subject.por.fl_str_mv |
Anãs brancas Fotometria astronômica |
topic |
Anãs brancas Fotometria astronômica White dwarfs Stars : Variables : General Starspots Binaries : Close |
dc.subject.eng.fl_str_mv |
White dwarfs Stars : Variables : General Starspots Binaries : Close |
description |
Context. About 10% of all stars exhibit absorption lines of ultra-highly excited (UHE) metals (e.g., O viii) in their optical spectra when entering the white dwarf cooling sequence. This is something that has never been observed in any other astrophysical object, and poses a decades-long mystery in our understanding of the late stages of stellar evolution. The recent discovery of a UHE white dwarf that is both spectroscopically and photometrically variable led to the speculation that the UHE lines might be created in a shock-heated circumstellar magnetosphere. Aims. We aim to gain a better understanding of these mysterious objects by studying the photometric variability of the whole popula tion of UHE white dwarfs, and white dwarfs showing only the He ii line problem, as both phenomena are believed to be connected. Methods. We investigate (multi-band) light curves from several ground- and space-based surveys of all 16 currently known UHE white dwarfs (including one newly discovered) and eight white dwarfs that show only the He ii line problem. Results. We find that 75+8 −13% of the UHE white dwarfs, and 75+9 −19% of the He ii line problem white dwarfs are significantly photo metrically variable, with periods ranging from 0.22 d to 2.93 d and amplitudes from a few tenths to a few hundredths of a magnitude. The high variability rate is in stark contrast to the variability rate amongst normal hot white dwarfs (we find 9+4 −2%), marking UHE and He ii line problem white dwarfs as a new class of variable stars. The period distribution of our sample agrees with both the orbital period distribution of post-common-envelope binaries and the rotational period distribution of magnetic white dwarfs if we assume that the objects in our sample will spin-up as a consequence of further contraction. Conclusions. We find further evidence that UHE and He ii line problem white dwarfs are indeed related, as concluded from their overlap in the Gaia HRD, similar photometric variability rates, light-curve shapes and amplitudes, and period distributions. The lack of increasing photometric amplitudes towards longer wavelengths, as well as the nondetection of optical emission lines arising from the highly irradiated face of a hypothetical secondary in the optical spectra of our stars, makes it seem unlikely that an irradiated late-type companion is the origin of the photometric variability. Instead, we believe that spots on the surfaces of these stars and/or geometrical effects of circumstellar material might be responsible. |
publishDate |
2021 |
dc.date.issued.fl_str_mv |
2021 |
dc.date.accessioned.fl_str_mv |
2022-04-13T04:51:47Z |
dc.type.driver.fl_str_mv |
Estrangeiro info:eu-repo/semantics/article |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
format |
article |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://hdl.handle.net/10183/237173 |
dc.identifier.issn.pt_BR.fl_str_mv |
0004-6361 |
dc.identifier.nrb.pt_BR.fl_str_mv |
001139574 |
identifier_str_mv |
0004-6361 001139574 |
url |
http://hdl.handle.net/10183/237173 |
dc.language.iso.fl_str_mv |
eng |
language |
eng |
dc.relation.ispartof.pt_BR.fl_str_mv |
Astronomy and astrophysics. Les Ulis. Vol. 647 (Apr. 2021), A184, 22 p. |
dc.rights.driver.fl_str_mv |
info:eu-repo/semantics/openAccess |
eu_rights_str_mv |
openAccess |
dc.format.none.fl_str_mv |
application/pdf |
dc.source.none.fl_str_mv |
reponame:Repositório Institucional da UFRGS instname:Universidade Federal do Rio Grande do Sul (UFRGS) instacron:UFRGS |
instname_str |
Universidade Federal do Rio Grande do Sul (UFRGS) |
instacron_str |
UFRGS |
institution |
UFRGS |
reponame_str |
Repositório Institucional da UFRGS |
collection |
Repositório Institucional da UFRGS |
bitstream.url.fl_str_mv |
http://www.lume.ufrgs.br/bitstream/10183/237173/2/001139574.pdf.txt http://www.lume.ufrgs.br/bitstream/10183/237173/1/001139574.pdf |
bitstream.checksum.fl_str_mv |
f3191a62405447308ed366f8bd629565 2cf672d7081d4434be872e41df0d0c13 |
bitstream.checksumAlgorithm.fl_str_mv |
MD5 MD5 |
repository.name.fl_str_mv |
Repositório Institucional da UFRGS - Universidade Federal do Rio Grande do Sul (UFRGS) |
repository.mail.fl_str_mv |
|
_version_ |
1801225054028038144 |