The confirmation and revision on the orbital period change of the possible type Ia supernova progenitor V617 Sagittarii

This work reports new photometric results of eclipsing cataclysmic variable V617 Sagittarii (V617 Sgr). We analyzed the orbital period change of V617 Sgr, by employing three new CCD eclipse timings since 2010 along with all the available data from the literature. It was found that the orbital period of V617 Sgr undergoes an obvious long-term increase, which confirms the result revealed by Steiner et al. (2006). The rate of orbital period increase was calculated to be ${\dot{P}}$ = +2.14(0.05) $\times$ 10$^{-7}$ day/year. This suggests the lifetime of the secondary star will attain to the end in a timescale of 0.97 $\times$ 10$^6$ years faster than that predicted previously. In particular, a cyclic variation with a period of 4.5 year and an amplitude of 2.3 minutes may present in the O-C diagram. Dominated by the wind-accretion mechanism, high mass transfer from the low mass secondary to the white dwarf is expected to sustain in the V Sge-type star V617 Sgr during its long-term evolution. The mass transfer rate $|\dot{M}_{tr}|$ was estimated to be in the range of about 2.2 $\times$ 10$^{-7}$ to 5.2 $\times$ 10$^{-7}$ M$_{\odot}$ yr$^{-1}$. Accordingly, the already massive ($\geq$ 1.2 M$_{\odot}$) white dwarf primary will process stable nuclear burning, accrete a fraction of mass from its companion to reach the standard Chandrasekhar mass limit ($\simeq$ 1.38 M$_{\odot}$), and ultimately produce a type Ia supernova (SN Ia) within about 4 $\sim$ 8 $\times$ 10$^{5}$ years or earlier.Comment: 5 pages, 2 figures, Accepted by PASJ on 20 August 201

Physical parameters of the O6.5V+B1V eclipsing binary system LS 1135

The 'All Sky Automated Survey' (ASAS) photometric observations of LS 1135, an O-type single-lined binary (SB1) system with an orbital period of 2.7 d, show that the system is also eclipsing. This prompted us to re-examine the spectra used in the previously published spectroscopic orbit. Our new analysis of the spectra obtained near quadratures, reveals the presence of faint lines of the secondary component. We present for the first time a double-lined radial velocity orbit and values of physical parameters of this binary system. These values were obtained by analysing the ASAS photometry jointly with the radial velocities of both components by performing a numerical model of this binary based on the Wilson-Devinney method. We obtained an orbital inclination i ∼ 68°.5. With this value of the inclination, we deduced masses M1 ∼ 30 ± l M⊙ and M2 ∼ 9 ± 1 M⊙, and radii R1 ∼ 12 ± 1 R ⊙ and R2 ∼ 5 ± 1R⊙ for primary and secondary components, respectively. Both the components are well inside their respective Roche lobes. Fixing the Teff of the primary to the value corresponding to its spectral type (O6.5V), the Teff obtained for the secondary component corresponds approximately to a spectral type of B1V. The mass ratio M2/M1 ∼ 0.3 is among the lowest known values for spectroscopic binaries with O-type components.Facultad de Ciencias Astronómicas y Geofísica

Evidence of a brown dwarf in the eclipsing dwarf nova Z Chamaeleonis

We presented three new CCD observations of light minima of Z Chamaeleonis. All 187 available times of light minimum including 37 photographic data are compiled, and a new orbital period analysis is made by means of the standard O - C technique. The O - C diagram of Z Chamaeleonis presents a cyclical periodic change of 32.57 yr with a high significance level. We attempted to apply two plausible mechanisms (i.e., Applegate's mechanism and light travel-time effect) to explain the cyclical variations of orbital period shown in the O-C diagram. Although the previous works suggested that solar-type magnetic cycles in the red dwarf are the best explanation, the analysis of Applegate's mechanism in this paper presents a negative result. Accordingly, a light travel-time effect is proposed, and a brown dwarf as a tertiary component orbiting around dwarf nova Z Chamaeleonis is derived with a significance level of ≳81.6%, which may be a plausible explanation of the periodic variation in the systemic velocity of Z Chamaeleonis in superoutburst.Facultad de Ciencias Astronómicas y Geofísica

Evidence of a brown dwarf in the eclipsing dwarf nova Z Chamaeleonis

We presented three new CCD observations of light minima of Z Chamaeleonis. All 187 available times of light minimum including 37 photographic data are compiled, and a new orbital period analysis is made by means of the standard O - C technique. The O - C diagram of Z Chamaeleonis presents a cyclical periodic change of 32.57 yr with a high significance level. We attempted to apply two plausible mechanisms (i.e., Applegate's mechanism and light travel-time effect) to explain the cyclical variations of orbital period shown in the O-C diagram. Although the previous works suggested that solar-type magnetic cycles in the red dwarf are the best explanation, the analysis of Applegate's mechanism in this paper presents a negative result. Accordingly, a light travel-time effect is proposed, and a brown dwarf as a tertiary component orbiting around dwarf nova Z Chamaeleonis is derived with a significance level of ≳81.6%, which may be a plausible explanation of the periodic variation in the systemic velocity of Z Chamaeleonis in superoutburst.Facultad de Ciencias Astronómicas y Geofísica

Confirmation and revision on the orbital period change of the possible type Ia supernova progenitor V617 Sagittarii

This work reports new photometric results of eclipsing cataclysmic variable V617 Sagittarii (V617 Sgr). We analyzed the orbital period change of V617 Sgr by employing three new (since 2010) CCD eclipse timings along with all the available data from the literature. It was found that the orbital period of V617 Sgr undergoes an obvious long-term increase, which confirms the result revealed by Steiner et al. (2006). The rate of orbital period increase was calculated to be P = +2.14(0.05) × 10-7 d yr-1. This suggests the lifetime of the secondary star will end in a timescale of 0.97 × 106 yr faster than that predicted previously. In particular, a cyclic variation with a period of 4.5 yr and an amplitude of 2.3 min may appear in the O - C diagram. Dominated by the wind-accretion mechanism, high mass transfer from the low mass secondary to the white dwarf is expected to continue in the V Sge-type star V617 Sgr during its long-term evolution. The mass transfer rate |Mtr| was estimated to be in the range of about 2.2 × 10-7 to 5.2 × 10-7 M⊙ yr-1. Accordingly, the already massive (≥ 1.2 M⊙) white dwarf primary will process stable nuclear burning, accrete a fraction of the mass from its companion to reach the standard Chandrasekhar mass limit (≃ 1.38 M⊙), and ultimately produce a type Ia supernova (SN Ia) within about 4-8 × 105 yr or earlier.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Physical parameters of the O6.5V+B1V eclipsing binary system LS 1135

The 'All Sky Automated Survey' (ASAS) photometric observations of LS 1135, an O-type single-lined binary (SB1) system with an orbital period of 2.7 d, show that the system is also eclipsing. This prompted us to re-examine the spectra used in the previously published spectroscopic orbit. Our new analysis of the spectra obtained near quadratures, reveals the presence of faint lines of the secondary component. We present for the first time a double-lined radial velocity orbit and values of physical parameters of this binary system. These values were obtained by analysing the ASAS photometry jointly with the radial velocities of both components by performing a numerical model of this binary based on the Wilson-Devinney method. We obtained an orbital inclination i ∼ 68°.5. With this value of the inclination, we deduced masses M1 ∼ 30 ± l M⊙ and M2 ∼ 9 ± 1 M⊙, and radii R1 ∼ 12 ± 1 R ⊙ and R2 ∼ 5 ± 1R⊙ for primary and secondary components, respectively. Both the components are well inside their respective Roche lobes. Fixing the Teff of the primary to the value corresponding to its spectral type (O6.5V), the Teff obtained for the secondary component corresponds approximately to a spectral type of B1V. The mass ratio M2/M1 ∼ 0.3 is among the lowest known values for spectroscopic binaries with O-type components.Facultad de Ciencias Astronómicas y Geofísica

Monitoring and analyzing exoplanetary transits from Argentina

Photometric observations of transits can be used to derive physical and orbital parameters of the system, like the planetary and stellar radius, orbital inclination and mean density of the star. Furthermore, monitoring possible periodic variations in transit timing of planets is important, since small changes can be caused by the presence of other planets or moons in the system. On the other hand, long term changes in the transit length can be due to the orbital precession of the planets. For these reasons we started an observational program dedicated to observe transits of known exoplanets with the aim of contributing to a better understanding of these planetary systems. In this work we present our first results obtained using the observational facilities in Argentina including the 2.15 telescope at CASLE

Orbital period analyses for two cataclysmic variables: UZ Fornacis and V348 Puppis inside the period gap

Four new CCD eclipse timings of the white dwarf for polar UZ Fornacis and six updated CCD mid-eclipse times for SW-Sex-type nova-like V348 Puppis are obtained. Detailed O-C analyses are made for both cataclysmic variables (CVs) inside the period gap. Orbital period increases at a rate of 2.63(±0.58) × 10-11 s s -1 for UZ For and 5.8(±1.9) × 10-12 s s -1 for V348 Pup, respectively, are discovered in their new O-C diagrams. However, conservative mass transfer from the secondary to the massive white dwarf cannot explain the observed orbital period increases for both CVs, which are regarded as part of modulations at longer periods. Moreover, the O-C diagram of UZ For shows a possible cyclical change with a period of 23.4(±5.1) yr. To explain the observed cyclical period changes in UZ For, both mechanisms of magnetic activity cycles in late-type secondaries and the light travel-time effect are regarded as probable causes. Not only does the modulation period of 23.4 yr obey the empirical correlation between Pmod and Ω, but also the estimated fractional period change δP/P ~ 7.3 × 10-7 displays a behaviour similar to that of CVs below the period gap. On the other hand, a calculation for the light travel-time effect implies with a high confidence level that the tertiary component in UZ For may be a brown dwarf, when the orbital inclination of the third body is larger than 16°.Facultad de Ciencias Astronómicas y Geofísica

A cyclical period variation detected in the updated orbital period analysis of TV Columbae

Two CCD photometries of the intermediate polar TV Columbae are made for obtaining two updated eclipse timings with high precision. There is an interval time ~17 yr since the last mid-eclipse time observed in 1991. Thus, the new mid-eclipse times might offer an opportunity to check the previous orbital ephemerides. A calculation indicates that the orbital ephemeris derived by Augusteijn et al. (Astron. Astrophys. Suppl. Ser. 107:219, 1994) should be corrected. Based on the proper linear ephemeris (Hellier in Mon. Not. R. Astron. Soc. 264:132, 1993), the new orbital period analysis suggests a cyclical period variation in the O-C diagram of TV Columbae. Using Applegate's mechanism to explain the periodic oscillation in the O-C diagram, the required energy is larger than the energy that a M0-type star can afford over a complete variation period of ~31.0(±3.0) yr. Thus, the light travel-time effect indicates that the tertiary component in TV Columbae may be a dwarf with a low mass, which is near the lower mass limit of ~0.08M⊙ as long as the inclination of the third body is high enough.Facultad de Ciencias Astronómicas y Geofísica

Monitoring and analyzing exoplanetary transits from Argentina

Photometric observations of transits can be used to derive physical and orbital parameters of the system, like the planetary and stellar radius, orbital inclination and mean density of the star. Furthermore, monitoring possible periodic variations in transit timing of planets is important, since small changes can be caused by the presence of other planets or moons in the system. On the other hand, long term changes in the transit length can be due to the orbital precession of the planets. For these reasons we started an observational program dedicated to observe transits of known exoplanets with the aim of contributing to a better understanding of these planetary systems. In this work we present our first results obtained using the observational facilities in Argentina including the 2.15 telescope at CASLEO.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica