Articles de revistahttp://hdl.handle.net/2117/11372024-03-28T22:11:18Z2024-03-28T22:11:18ZThe unusual planetary nebula nucleus in the Galactic open cluster M37 and six further hot white dwarf candidatesWerner, KlausReindl, NicoleRaddi, RobertoGriggio, MassimoBedin, LuigiCamisassa, María EugeniaRebassa Mansergas, AlbertoTorres Gil, SantiagoGoodhew, Peterhttp://hdl.handle.net/2117/4050782024-03-25T01:42:26Z2024-03-21T12:01:43ZThe unusual planetary nebula nucleus in the Galactic open cluster M37 and six further hot white dwarf candidates
Werner, Klaus; Reindl, Nicole; Raddi, Roberto; Griggio, Massimo; Bedin, Luigi; Camisassa, María Eugenia; Rebassa Mansergas, Alberto; Torres Gil, Santiago; Goodhew, Peter
Planetary nebulae in Galactic open star clusters are rare objects; only three are known to date. They are of particular interest because their distance can be determined with high accuracy, allowing one to characterize the physical properties of the planetary nebula and its ionizing central star with high confidence. Here we present the first quantitative spectroscopic analysis of a central star in an open cluster, namely the faint nucleus of IPHASX J055226.2+323724 in M37. This cluster contains 14 confirmed white dwarf members, which were previously used to study the initial-to-final-mass relation of white dwarfs, and six additional white dwarf candidates. We performed an atmosphere modeling of spectra taken with the 10m Gran Telescopio Canarias. The central star is a hot hydrogen-deficient white dwarf with an effective temperature of 90 000 K and spectral type PG1159 (helium- and carbon-rich). We know it is about to transform into a helium-rich DO white dwarf because the relatively low atmospheric carbon abundance indicates ongoing gravitational settling of heavy elements. The star belongs to a group of hot white dwarfs that exhibit ultrahigh-excitation spectral lines possibly emerging from shock-heated material in a magnetosphere. We find a relatively high stellar mass of M = 0.85-0.14+0.13 M¿. This young white dwarf is important for the semi-empirical initial-final mass relation because any uncertainty related to white-dwarf cooling theory is insignificant with respect to the pre-white-dwarf timescale. Its post-asymptotic-giant-branch age of 170 000–480 000 yr suggests that the extended planetary nebula is extraordinarily old. We also performed a spectroscopic analysis of the six other white dwarf candidates of M37, confirming one as a cluster member.
2024-03-21T12:01:43ZWerner, KlausReindl, NicoleRaddi, RobertoGriggio, MassimoBedin, LuigiCamisassa, María EugeniaRebassa Mansergas, AlbertoTorres Gil, SantiagoGoodhew, PeterPlanetary nebulae in Galactic open star clusters are rare objects; only three are known to date. They are of particular interest because their distance can be determined with high accuracy, allowing one to characterize the physical properties of the planetary nebula and its ionizing central star with high confidence. Here we present the first quantitative spectroscopic analysis of a central star in an open cluster, namely the faint nucleus of IPHASX J055226.2+323724 in M37. This cluster contains 14 confirmed white dwarf members, which were previously used to study the initial-to-final-mass relation of white dwarfs, and six additional white dwarf candidates. We performed an atmosphere modeling of spectra taken with the 10m Gran Telescopio Canarias. The central star is a hot hydrogen-deficient white dwarf with an effective temperature of 90 000 K and spectral type PG1159 (helium- and carbon-rich). We know it is about to transform into a helium-rich DO white dwarf because the relatively low atmospheric carbon abundance indicates ongoing gravitational settling of heavy elements. The star belongs to a group of hot white dwarfs that exhibit ultrahigh-excitation spectral lines possibly emerging from shock-heated material in a magnetosphere. We find a relatively high stellar mass of M = 0.85-0.14+0.13 M¿. This young white dwarf is important for the semi-empirical initial-final mass relation because any uncertainty related to white-dwarf cooling theory is insignificant with respect to the pre-white-dwarf timescale. Its post-asymptotic-giant-branch age of 170 000–480 000 yr suggests that the extended planetary nebula is extraordinarily old. We also performed a spectroscopic analysis of the six other white dwarf candidates of M37, confirming one as a cluster member.NICER Observations of thermonuclear bursts from 4U 1728-34: detection of oscillations prior to the onset of two burstsBostanci, FundaBoztepe, TugbaGüver, TolgaStrohmayer, Tod E.Cavecchi, YuriGögüs, ErsinAltamirano, DiegoBult, PeterChakrabarty, DeeptoGuillot, SebastienJaisawal, Gaurava K.Malacaria, ChristianMancuso, Giulio C.Sanna, AndreaSwank, Jean H.http://hdl.handle.net/2117/4034072024-03-20T11:57:35Z2024-02-28T17:23:41ZNICER Observations of thermonuclear bursts from 4U 1728-34: detection of oscillations prior to the onset of two bursts
Bostanci, Funda; Boztepe, Tugba; Güver, Tolga; Strohmayer, Tod E.; Cavecchi, Yuri; Gögüs, Ersin; Altamirano, Diego; Bult, Peter; Chakrabarty, Deepto; Guillot, Sebastien; Jaisawal, Gaurava K.; Malacaria, Christian; Mancuso, Giulio C.; Sanna, Andrea; Swank, Jean H.
We present temporal and time-resolved spectral analyses of all the thermonuclear X-ray bursts observed from the neutron star low-mass X-ray binary 4U 1728-34 with NICER from 2017 June to 2019 September. In total, we detected 11 X-ray bursts from the source and performed time-resolved spectroscopy. Unlike some of the earlier results for other bursting sources from NICER, our spectral results indicate that the use of a scaling factor for the persistent emission is not statistically necessary. This is primarily a result of the strong interstellar absorption in the line of sight toward 4U 1728-34, which causes the count rates to be significantly lower at low energies. We also searched for burst oscillations and detected modulations in six different bursts at around the previously known burst oscillation frequency of 363 Hz. Finally, we report the detection of oscillations prior to two bursts at 356 and 359 Hz, respectively. This is the first time in the literature where burst oscillations are detected before the rapid rise in X-ray flux, from any known burster. These oscillations disappear as soon as the burst starts to rise and occur at a somewhat lower frequency than the oscillations we detect during the bursts.
2024-02-28T17:23:41ZBostanci, FundaBoztepe, TugbaGüver, TolgaStrohmayer, Tod E.Cavecchi, YuriGögüs, ErsinAltamirano, DiegoBult, PeterChakrabarty, DeeptoGuillot, SebastienJaisawal, Gaurava K.Malacaria, ChristianMancuso, Giulio C.Sanna, AndreaSwank, Jean H.We present temporal and time-resolved spectral analyses of all the thermonuclear X-ray bursts observed from the neutron star low-mass X-ray binary 4U 1728-34 with NICER from 2017 June to 2019 September. In total, we detected 11 X-ray bursts from the source and performed time-resolved spectroscopy. Unlike some of the earlier results for other bursting sources from NICER, our spectral results indicate that the use of a scaling factor for the persistent emission is not statistically necessary. This is primarily a result of the strong interstellar absorption in the line of sight toward 4U 1728-34, which causes the count rates to be significantly lower at low energies. We also searched for burst oscillations and detected modulations in six different bursts at around the previously known burst oscillation frequency of 363 Hz. Finally, we report the detection of oscillations prior to two bursts at 356 and 359 Hz, respectively. This is the first time in the literature where burst oscillations are detected before the rapid rise in X-ray flux, from any known burster. These oscillations disappear as soon as the burst starts to rise and occur at a somewhat lower frequency than the oscillations we detect during the bursts.Main-sequence companions to white dwarfs - II. The age-activity-rotation relation from a sample of Gaia common proper motion pairsRebassa Mansergas, AlbertoMaldonado, JesúsRaddi, RobertoTorres Gil, SantiagoHoskin, MatthewCunningham, TimHollands, MarkRen, JuanjuanGänsicke, Boris T.Tremblay, P. E.Camisassa, María Eugeniahttp://hdl.handle.net/2117/3991082024-01-17T13:10:32Z2024-01-10T16:31:24ZMain-sequence companions to white dwarfs - II. The age-activity-rotation relation from a sample of Gaia common proper motion pairs
Rebassa Mansergas, Alberto; Maldonado, Jesús; Raddi, Roberto; Torres Gil, Santiago; Hoskin, Matthew; Cunningham, Tim; Hollands, Mark; Ren, Juanjuan; Gänsicke, Boris T.; Tremblay, P. E.; Camisassa, María Eugenia
Magnetic activity and rotation are related to the age of low-mass main-sequence stars. To further constrain these relations, we
study a sample of 574 main-sequence stars members of common proper motion pairs with white dwarfs, identified thanks to
Gaia astrometry. We use the white dwarfs as age indicators, while the activity indexes and rotational velocities are obtained
from the main-sequence companions using standard procedures. We find that stars older than 5 Gyr do not display H a nor
Ca II H&K emission unless they are fast rotators due to tidal locking from the presence of unseen companions and that the
rotational velocities tend to decrease over time, thus supporting the so-called gyrochronology. However, we also find moderately
old stars (2–6 Gyr) that are active presumably because they rotate faster than they should for their given ages. This indicates
that they may be suffering from weakened magnetic braking or that they possibly evolved through wind accretion processes in
the past. The activity fractions that we measure for all stars younger than 5 Gyr range between 10 and 40 per cent. This is line
with the expectations, since our sample is composed of F, G, K, and early M stars, which are thought to have short (<2 Gyr)
activity lifetimes. Finally, we observe that the H a fractional luminosities and the RHK indexes for our sample of (slowly rotating)
stars show a spread (-4 >log(LH a/Lbol); log(RHK) > -5) typically found in inactive M stars or weakly active/inactive F, G, K
stars.
2024-01-10T16:31:24ZRebassa Mansergas, AlbertoMaldonado, JesúsRaddi, RobertoTorres Gil, SantiagoHoskin, MatthewCunningham, TimHollands, MarkRen, JuanjuanGänsicke, Boris T.Tremblay, P. E.Camisassa, María EugeniaMagnetic activity and rotation are related to the age of low-mass main-sequence stars. To further constrain these relations, we
study a sample of 574 main-sequence stars members of common proper motion pairs with white dwarfs, identified thanks to
Gaia astrometry. We use the white dwarfs as age indicators, while the activity indexes and rotational velocities are obtained
from the main-sequence companions using standard procedures. We find that stars older than 5 Gyr do not display H a nor
Ca II H&K emission unless they are fast rotators due to tidal locking from the presence of unseen companions and that the
rotational velocities tend to decrease over time, thus supporting the so-called gyrochronology. However, we also find moderately
old stars (2–6 Gyr) that are active presumably because they rotate faster than they should for their given ages. This indicates
that they may be suffering from weakened magnetic braking or that they possibly evolved through wind accretion processes in
the past. The activity fractions that we measure for all stars younger than 5 Gyr range between 10 and 40 per cent. This is line
with the expectations, since our sample is composed of F, G, K, and early M stars, which are thought to have short (<2 Gyr)
activity lifetimes. Finally, we observe that the H a fractional luminosities and the RHK indexes for our sample of (slowly rotating)
stars show a spread (-4 >log(LH a/Lbol); log(RHK) > -5) typically found in inactive M stars or weakly active/inactive F, G, K
stars.First measurement of the low-energy direct capture in Ne 20 (p,¿) Na 21 and improved energy and strength of the Ec.m.=368 keV resonanceMasha, ElianaBarbieri, LuciaSkowronski, JakubAliotta, MarialuisaAnanna, ChemseddineBarile, FrancescoBemmerer, DanielBest, AndreasBoeltzig, AxelBroggini, CarloBruno, CarloCaciolli, AntonioJosé Pont, Jordihttp://hdl.handle.net/2117/3983592023-12-24T22:24:56Z2023-12-19T18:45:27ZFirst measurement of the low-energy direct capture in Ne 20 (p,¿) Na 21 and improved energy and strength of the Ec.m.=368 keV resonance
Masha, Eliana; Barbieri, Lucia; Skowronski, Jakub; Aliotta, Marialuisa; Ananna, Chemseddine; Barile, Francesco; Bemmerer, Daniel; Best, Andreas; Boeltzig, Axel; Broggini, Carlo; Bruno, Carlo; Caciolli, Antonio; José Pont, Jordi
The 20Ne(p,¿)21Na reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below Ec.m.=352 keV, and of the contribution from the Ec.m.=368 keV resonance, which dominates the reaction rate at T=0.03–1.00 GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt ¿ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ¿¿=(0.112±0.002stat±0.005sys)meV, with an uncertainty a factor of 3 smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at T<0.1 GK and agrees with previous estimates at temperatures T=0.1 GK. Initial astrophysical implications are presented.
2023-12-19T18:45:27ZMasha, ElianaBarbieri, LuciaSkowronski, JakubAliotta, MarialuisaAnanna, ChemseddineBarile, FrancescoBemmerer, DanielBest, AndreasBoeltzig, AxelBroggini, CarloBruno, CarloCaciolli, AntonioJosé Pont, JordiThe 20Ne(p,¿)21Na reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below Ec.m.=352 keV, and of the contribution from the Ec.m.=368 keV resonance, which dominates the reaction rate at T=0.03–1.00 GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt ¿ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ¿¿=(0.112±0.002stat±0.005sys)meV, with an uncertainty a factor of 3 smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at T<0.1 GK and agrees with previous estimates at temperatures T=0.1 GK. Initial astrophysical implications are presented.Confirmation of a new resonance in Si 26 and contribution of classical novae to the galactic abundance of Al 26Canete, LaetitiaDoherty, DanielLotay, GavinSeweryniak, DariuszCampbell, ChrisCarpenter, Michael PattenCatford, WiltonChipps, Kelly A.Henderson, JackIzzard, RobertJanssens, RobertJayatissa, HeshaniJosé Pont, Jordihttp://hdl.handle.net/2117/3983522023-12-24T22:25:54Z2023-12-19T18:26:00ZConfirmation of a new resonance in Si 26 and contribution of classical novae to the galactic abundance of Al 26
Canete, Laetitia; Doherty, Daniel; Lotay, Gavin; Seweryniak, Dariusz; Campbell, Chris; Carpenter, Michael Patten; Catford, Wilton; Chipps, Kelly A.; Henderson, Jack; Izzard, Robert; Janssens, Robert; Jayatissa, Heshani; José Pont, Jordi
The 25Al(p,¿) reaction has long been highlighted as a possible means to bypass the production of 26Al cosmic ¿ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in 26Si have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed ¿-ray spectroscopy study of 26Si and present evidence for the existence of a new, likely l=1, resonance in the 25Al + p system at Er=153.9(15) keV. This state is now expected to provide the dominant contribution to the 25Al(p,¿) stellar reaction rate over the temperature range, T˜0.1-0.2 GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of 26Al from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed galactic abundance of 26Al is ˜0.2M¿. Finally, we briefly highlight the important role that super-asymptotic giant branch stars may play in the production of 26Al.
2023-12-19T18:26:00ZCanete, LaetitiaDoherty, DanielLotay, GavinSeweryniak, DariuszCampbell, ChrisCarpenter, Michael PattenCatford, WiltonChipps, Kelly A.Henderson, JackIzzard, RobertJanssens, RobertJayatissa, HeshaniJosé Pont, JordiThe 25Al(p,¿) reaction has long been highlighted as a possible means to bypass the production of 26Al cosmic ¿ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in 26Si have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed ¿-ray spectroscopy study of 26Si and present evidence for the existence of a new, likely l=1, resonance in the 25Al + p system at Er=153.9(15) keV. This state is now expected to provide the dominant contribution to the 25Al(p,¿) stellar reaction rate over the temperature range, T˜0.1-0.2 GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of 26Al from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed galactic abundance of 26Al is ˜0.2M¿. Finally, we briefly highlight the important role that super-asymptotic giant branch stars may play in the production of 26Al.Nuclear physics midterm plan at LNSAgodi, ClementinaCappuzzello, FrancescoCardella, GiuseppeCirrone, PabloDe Filippo, Enricodi Pietro, AlessiaGargano, Angelala Cognata, MarcoMascali, DavidMilluzzo, GiulianaNania, RosarioJosé Pont, Jordihttp://hdl.handle.net/2117/3983422023-12-24T22:29:11Z2023-12-19T17:43:38ZNuclear physics midterm plan at LNS
Agodi, Clementina; Cappuzzello, Francesco; Cardella, Giuseppe; Cirrone, Pablo; De Filippo, Enrico; di Pietro, Alessia; Gargano, Angela; la Cognata, Marco; Mascali, David; Milluzzo, Giuliana; Nania, Rosario; José Pont, Jordi
The next years will see the completion of several new facilities at Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud (LNS) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics and applications. These include a new line for high-intensity cyclotron beams, a new facility for in-flight production of radioactive ion beams, the PANDORA plasma trap for multidisciplinary studies and a high-power laser for basic science and applied physics. The nuclear physics community has organized a workshop to discuss the new physics opportunities that will be possible in the middle term (5–7 years) by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report.
2023-12-19T17:43:38ZAgodi, ClementinaCappuzzello, FrancescoCardella, GiuseppeCirrone, PabloDe Filippo, Enricodi Pietro, AlessiaGargano, Angelala Cognata, MarcoMascali, DavidMilluzzo, GiulianaNania, RosarioJosé Pont, JordiThe next years will see the completion of several new facilities at Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud (LNS) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics and applications. These include a new line for high-intensity cyclotron beams, a new facility for in-flight production of radioactive ion beams, the PANDORA plasma trap for multidisciplinary studies and a high-power laser for basic science and applied physics. The nuclear physics community has organized a workshop to discuss the new physics opportunities that will be possible in the middle term (5–7 years) by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report.Sub-second infrared variability from the archetypal accreting neutron star 4U 1728-34Vincentelli, FedericoCasella, PiergiorgioBorghese, AliceCavecchi, YuriMastroserio, GuglielmoStella, LuigiAltamirano, DiegoArmas Padilla, MontserratBaglio, Maria CristinaBelloni, FabioCasares, JorgeCúneo, VirginiaDegenaar, Nathaliehttp://hdl.handle.net/2117/3979532023-12-17T05:47:34Z2023-12-13T15:45:37ZSub-second infrared variability from the archetypal accreting neutron star 4U 1728-34
Vincentelli, Federico; Casella, Piergiorgio; Borghese, Alice; Cavecchi, Yuri; Mastroserio, Guglielmo; Stella, Luigi; Altamirano, Diego; Armas Padilla, Montserrat; Baglio, Maria Cristina; Belloni, Fabio; Casares, Jorge; Cúneo, Virginia; Degenaar, Nathalie
We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed ¿h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM–Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ¿ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of ¿s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than ¿h and an inclination higher than 8¿.
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record Vincentelli, F., et al. Sub-second infrared variability from the archetypal accreting neutron star 4U 1728-34. Monthly notices of the Royal Astronomical Society, October 2023, vol. 525, n. 2, p. 2509-2518. is available online at: https://doi.org/10.1093/mnras/stad2414
2023-12-13T15:45:37ZVincentelli, FedericoCasella, PiergiorgioBorghese, AliceCavecchi, YuriMastroserio, GuglielmoStella, LuigiAltamirano, DiegoArmas Padilla, MontserratBaglio, Maria CristinaBelloni, FabioCasares, JorgeCúneo, VirginiaDegenaar, NathalieWe report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed ¿h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM–Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ¿ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of ¿s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than ¿h and an inclination higher than 8¿.General relativistic pulsations of ultra-massive ZZ Ceti starsCórsico, Alejandro H.Boston, ReeceAlthaus, Leandro G.Kilic, MukreminKepler, Souza OliveiraCamisassa, María EugeniaTorres Gil, Santiagohttp://hdl.handle.net/2117/3979512023-12-17T05:45:37Z2023-12-13T15:13:07ZGeneral relativistic pulsations of ultra-massive ZZ Ceti stars
Córsico, Alejandro H.; Boston, Reece; Althaus, Leandro G.; Kilic, Mukremin; Kepler, Souza Oliveira; Camisassa, María Eugenia; Torres Gil, Santiago
Ultra-massive white dwarf stars are currently being discovered at a considerable rate, thanks to surveys such as the Gaia space mission. These dense and compact stellar remnants likely play a major role in Type Ia supernova explosions. It is possible to probe the interiors of ultra-massive white dwarfs through asteroseismology. In the case of the most massive white dwarfs, general relativity could affect their structure and pulsations substantially. In this work, we present results of relativistic pulsation calculations employing relativistic ultra-massive ONe-core white dwarf models with hydrogen-rich atmospheres and masses ranging from 1.29 to 1.369 M¿ with the aim of assessing the impact of general relativity on the adiabatic gravity (g)-mode period spectrum of very high mass ZZ Ceti stars. Employing the relativistic Cowling approximation for the pulsation analysis, we find that the critical buoyancy (Brunt–Väisälä) and acoustic (Lamb) frequencies are larger for the relativistic case, compared to the Newtonian case, due to the relativistic white dwarf models having smaller radii and higher gravities for a fixed stellar mass. In addition, the g-mode periods are shorter in the relativistic case than those in the Newtonian computations, with relative differences of up to ~50 per¿cent for the highest mass models (¿1.369 M¿ ¿) and for effective temperatures typical of the ZZ Ceti instability strip. Hence, the effects of general relativity on the structure, evolution, and pulsations of white dwarfs with masses larger than ~1.29 M¿ cannot be ignored in the asteroseismological analysis of ultra-massive ZZ Ceti stars.
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record Córsico, A.H., et al. General relativistic pulsations of ultra-massive ZZ Ceti stars. Monthly notices of the Royal Astronomical Society, October 2023, vol. 524, n. 4, p. 5929-5943 is available online at: https://doi.org/10.1093/mnras/stad2248
2023-12-13T15:13:07ZCórsico, Alejandro H.Boston, ReeceAlthaus, Leandro G.Kilic, MukreminKepler, Souza OliveiraCamisassa, María EugeniaTorres Gil, SantiagoUltra-massive white dwarf stars are currently being discovered at a considerable rate, thanks to surveys such as the Gaia space mission. These dense and compact stellar remnants likely play a major role in Type Ia supernova explosions. It is possible to probe the interiors of ultra-massive white dwarfs through asteroseismology. In the case of the most massive white dwarfs, general relativity could affect their structure and pulsations substantially. In this work, we present results of relativistic pulsation calculations employing relativistic ultra-massive ONe-core white dwarf models with hydrogen-rich atmospheres and masses ranging from 1.29 to 1.369 M¿ with the aim of assessing the impact of general relativity on the adiabatic gravity (g)-mode period spectrum of very high mass ZZ Ceti stars. Employing the relativistic Cowling approximation for the pulsation analysis, we find that the critical buoyancy (Brunt–Väisälä) and acoustic (Lamb) frequencies are larger for the relativistic case, compared to the Newtonian case, due to the relativistic white dwarf models having smaller radii and higher gravities for a fixed stellar mass. In addition, the g-mode periods are shorter in the relativistic case than those in the Newtonian computations, with relative differences of up to ~50 per¿cent for the highest mass models (¿1.369 M¿ ¿) and for effective temperatures typical of the ZZ Ceti instability strip. Hence, the effects of general relativity on the structure, evolution, and pulsations of white dwarfs with masses larger than ~1.29 M¿ cannot be ignored in the asteroseismological analysis of ultra-massive ZZ Ceti stars.The orbital period of the recurrent nova V2487 Oph revealedRodríguez Gil, PabloCorral Santana, Jesus M.Elias Rosa, NancyGänsicke, Boris T.Hernanz, MargaritaSala Cladellas, Glòriahttp://hdl.handle.net/2117/3974332023-12-03T21:15:18Z2023-11-30T14:35:22ZThe orbital period of the recurrent nova V2487 Oph revealed
Rodríguez Gil, Pablo; Corral Santana, Jesus M.; Elias Rosa, Nancy; Gänsicke, Boris T.; Hernanz, Margarita; Sala Cladellas, Glòria
We present the first reliable determination of the orbital period of the recurrent nova V2487 Oph (Nova Oph 1998). We derived a value of 0.753 ± 0.016 d (18.1 ± 0.4 h) from the radial velocity curve of the intense He¿II ¿4686 emission line as detected in time-series X-shooter spectra. The orbital period is significantly shorter than earlier claims, but it makes V2487 Oph one of the longest period cataclysmic variables known. The spectrum of V2487 Oph is prolific in broad Balmer absorptions that resemble a white dwarf spectrum. However, we show that they come from the accretion disc viewed at low inclination. Although highly speculative, the analysis of the radial velocity curves provides a binary mass ratio q ˜ 0.16 and a donor star mass M2 ˜ 0.21 M¿, assuming the reported white dwarf mass M1 = 1.35 M¿. A subgiant M-type star is tentatively suggested as the donor star. We were lucky to inadvertently take some of the spectra when V2487 Oph was in a flare state. During the flare, we detected high-velocity emission in the Balmer and He¿II ¿4686 lines exceeding -2000 km s-1 at close to orbital phase 0.4. Receding emission up to 1200 km s-1 at about phase 0.3 is also observed. The similarities with the magnetic cataclysmic variables may point to magnetic accretion on to the white dwarf during the repeating flares.
2023-11-30T14:35:22ZRodríguez Gil, PabloCorral Santana, Jesus M.Elias Rosa, NancyGänsicke, Boris T.Hernanz, MargaritaSala Cladellas, GlòriaWe present the first reliable determination of the orbital period of the recurrent nova V2487 Oph (Nova Oph 1998). We derived a value of 0.753 ± 0.016 d (18.1 ± 0.4 h) from the radial velocity curve of the intense He¿II ¿4686 emission line as detected in time-series X-shooter spectra. The orbital period is significantly shorter than earlier claims, but it makes V2487 Oph one of the longest period cataclysmic variables known. The spectrum of V2487 Oph is prolific in broad Balmer absorptions that resemble a white dwarf spectrum. However, we show that they come from the accretion disc viewed at low inclination. Although highly speculative, the analysis of the radial velocity curves provides a binary mass ratio q ˜ 0.16 and a donor star mass M2 ˜ 0.21 M¿, assuming the reported white dwarf mass M1 = 1.35 M¿. A subgiant M-type star is tentatively suggested as the donor star. We were lucky to inadvertently take some of the spectra when V2487 Oph was in a flare state. During the flare, we detected high-velocity emission in the Balmer and He¿II ¿4686 lines exceeding -2000 km s-1 at close to orbital phase 0.4. Receding emission up to 1200 km s-1 at about phase 0.3 is also observed. The similarities with the magnetic cataclysmic variables may point to magnetic accretion on to the white dwarf during the repeating flares.Search for 22Na in novae supported by a novel method for measuring femtosecond nuclear lifetimesFougères, Chloéde Oliveira Santos, FrançoisJosé Pont, JordiMichelagnoli, CaterinaClément, EmmanuelKim, Yung HeeLemasson, AntoineGuimarães, ValdirBarrientos, DiegoBemmerer, DanielBenzoni, GiovannaBoston, Andrew J.http://hdl.handle.net/2117/3966422023-11-20T01:17:16Z2023-11-17T14:54:02ZSearch for 22Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes
Fougères, Chloé; de Oliveira Santos, François; José Pont, Jordi; Michelagnoli, Caterina; Clément, Emmanuel; Kim, Yung Hee; Lemasson, Antoine; Guimarães, Valdir; Barrientos, Diego; Bemmerer, Daniel; Benzoni, Giovanna; Boston, Andrew J.
Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26Al and 22Na. While ¿ rays from the decay of the former radioisotope have been observed throughout the Galaxy, 22Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV ¿-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The 22Na(p,¿¿)23Mg reaction remains the only source of large uncertainty about the amount of 22Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in 23Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the 23Mg states, places strong limits on the amount of 22Na produced in novae and constrains its detectability with future space-borne observatories.
2023-11-17T14:54:02ZFougères, Chloéde Oliveira Santos, FrançoisJosé Pont, JordiMichelagnoli, CaterinaClément, EmmanuelKim, Yung HeeLemasson, AntoineGuimarães, ValdirBarrientos, DiegoBemmerer, DanielBenzoni, GiovannaBoston, Andrew J.Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26Al and 22Na. While ¿ rays from the decay of the former radioisotope have been observed throughout the Galaxy, 22Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV ¿-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The 22Na(p,¿¿)23Mg reaction remains the only source of large uncertainty about the amount of 22Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in 23Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the 23Mg states, places strong limits on the amount of 22Na produced in novae and constrains its detectability with future space-borne observatories.