Person: Luna, Gerardo Juan Manuel
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23/12/1976
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Luna
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Gerardo Juan Manuel
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Publication NICER Monitoring of Supersoft X-Ray Sources(IOP Publishing, 2022) Luna, Gerardo Juan ManuelWe monitored four supersoft sources - two persistent ones, CAL 83 and MR Vel, and the recent novae YZ Ret (Nova Ret 2020), and V1674 Her (Nova Her 2021) - with NICER. The two persistent supersoft X-ray sources (SSS) were observed with unvaried X-ray flux level and spectrum, respectively, 13 and 20 yr after the last observations. Short-period modulations of the SSS appear where the spectrum of the luminous central source was fully visible (in CAL 83 and V1674 Her) and were absent in YZ Ret and MR Vel, in which the flux originated in photoionized or shocked plasma, while the white dwarf (WD) was not observable. We thus suggest that the pulsations occur on, or very close to, the WD surface. The pulsations of CAL 83 were almost unvaried after 15 yr, including an irregular drift of the ≃67 s period by 2.1 s. Simulations, including previous XMM-Newton data, indicate actual variations in period length within hours, rather than an artifact of the variable amplitude of the pulsations. Large amplitude pulsations with a period of 501.53 ± 0.30 s were always detected in V1674 Her, as long as the SSS was observable. This period seems to be due to rotation of a highly magnetized WD. We cannot confirm the maximum effective temperature of (≃145,000 K) previously inferred for this nova, and discuss the difficulty in interpreting its spectrum. The WD appears to present two surface zones, one of which does not emit SSS fluxPublication Expanding Bipolar X-Ray Structure after the 2006 Eruption of RS Oph(IOP Publishing, 2023) Luna, Gerardo Juan ManuelWe report on the detection and analysis of extended X-ray emission by the {\it Chandra} X-ray Observatory stemming from the 2006 eruption of the recurrent novae RS Oph. The extended emission was detected 1254 and 1927 days after the start of the 2006 eruption and is consistent with a bipolar flow oriented in the east-west direction of the sky with opening angles of approximately 70∘. The length of both lobes appeared to expand from 1.3 arcsec in 2009 to 2.0 arcsec in 2011, suggesting a projected expansion rate of 1.1±0.1 mas day−1 and an expansion velocity of 4600 km s−1 (D/2.4 kpc) in the plane of the sky. This expansion rate is consistent with previous estimates from optical and radio observations of material in a similar orientation. The X-ray emission does not show any evidence of cooling between 2009 and 2011, consistent with free expansion of the material. This discovery suggests that some mechanism collimates ejecta away from the equatorial plane, and that after that material passes through the red-giant wind, it expands freely into the cavity left by the 1985 eruption. We expect similar structures to arise from latest eruption and to expand into the cavity shaped by the 2006 eruption.Publication Optical spectroscopy and X-ray observations of the D-type symbiotic star EF Aql(Wiley Blackwell, 2020) Stoyanov, K. A.; Ilkiewicz, K.; Mikołajewska, J.; Mukai, K.; Martí, J; Latev, G; Boeva, S.; Zamanov, R. K.; Luna, Gerardo Juan ManuelWe performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with the Southern African Large Telescope (SALT), we determine the temperature (∼55 000 K) and the luminosity (∼5.3 L⊙) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements.We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10-12 erg cm-2 s-1, whichmeans that EF Aql is consistent with the faintestX-ray systems detected so far. Otherwise we detected it with the UltraViolet and Optical Telescope (UVOT) instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4 ± 0.3 d caused by the pulsations of the Mira-type donor star.