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Register a new userMultiwavelength optical observations of chromospherically active binary systems V. FF UMa (2RE J0933+624): a system with orbital period variation
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M.C. Galvez
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This is the fifth paper in a series aimed at studying the chromospheres of active binary systems using several optical spectroscopic indicators to obtain or improve orbital solution and fundamental stellar parameters. We present here the study of FF UMa (2RE J0933+624), a recently discovered, X-ray/EUV selected, active binary with strong H_alpha emission. The objectives of this work are, to find orbital solutions and define stellar parameters from precise radial velocities and carry out an extensive study of the optical indicators of chromospheric activity. We obtained high resolution echelle spectroscopic observations during five observing runs from 1998 to 2004. We found radial velocities by cross correlation with radial velocity standard stars to achieve the best orbital solution. We also measured rotational velocity by cross-correlation techniques and have studied the kinematic by galactic space- velocity components (U, V, W) and Eggen criteria. Finally, we have determined the chromospheric contribution in optical spectroscopic indicators, from Ca II H & K to Ca II IRT lines, using the spectral subtraction technique. We have found that this system presents an orbital period variation, higher than previously detected in other RS CVn systems. We determined an improved orbital solution, finding a circular orbit with a period of 3.274 days. We derived the stellar parameters, confirming the subgiant nature of the primary component and obtained rotational velocities (vsini), of 33.57 km/s and 32.38 km/s for the primary and secondary components respectively. From our kinematic study, we can deduce its membership to the Castor moving group. Finally, the activity study has given us a better understanding of the possible mechanisms that produce the orbital period variation.
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We present high resolution echelle spectra taken during four observing runs from 1999 to 2001 of the recently X-ray/EUV selected chromospherically active binary BK Psc (2RE J0039+103). Our observations confirm the single-lined spectroscopic binary(SB1) nature of this system and allow us to obtain, for the first time,the orbital solution of the system as in the case of a SB2 system. We have determined precise radial velocities of both components: for the primary by using the cross correlation technique, and for the secondary by using its chromospheric emission lines. We have obtained a circular orbit with an orbital period of 2.1663 days, very close to its photometric period of 2.24 days (indicating synchronous rotation). The spectral type (K5V) we determined for our spectra and the mass ratio (1.8) and minimum masses (Msin^{3}i) resulting from the orbital solution are compatible with the observed K5V primary and an unseen M3V secondary. Using this spectral classification, the projected rotational velocity (vsini, of 17.1 km/s}) obtained from the width of the cross-correlation function and the data provided by Hipparcos, we have derived other fundamental stellar parameters. The kinematics and the non-detection of the LiI line indicate that it is an old star. The analysis of the optical chromospheric activity indicators from the CaII H & K to CaII IRT lines, by using the spectral subtraction technique, indicates that both components of the binary system show high levels of chromospheric activity. H_alpha emission above the continuum from both components is a persistent feature of this system during the period 1999 to 2001 of our observations as well as in previous observations.
This paper describes a multiwavelengh optical study of chromospheres in two X-ray/EUV selected active binary stars with strong H_alpha emission, V789 Mon (2RE J0725-002) and GZ Leo (2RE J1101+223). The goal of the study is to determine radial velocities and fundamental stellar parameters in chromospherically active binary systems in order to include them in the activity-rotation and activity-age relations. We carried out high resolution echelle spectroscopic observations and applied spectral subtraction technique in order to measure emission excesses due to chromosphere. The detailed study of activity indicators allowed us to characterize the presence of different chromospheric features in these systems and enabled to include them in a larger activity-rotation survey. We computed radial velocities of the systems using cross correlation with the radial velocity standards. The double-line spectral binarity was confirmed and the orbital solutions improved for both systems. In addition, other stellar parameters such as: spectral types, projected rotational velocities (vsini), and the equivalent width of the lithium LiI 6707.8 AA absorption line were determined.
2RE J0743+224 (BD +23 1799) is a chromospherically active star selected by X-rays and EUV emission detected in the Einstein Slew Survey and ROSAT Wide Field Camara (WFC) all sky survey, and classified as single-lined spectroscopic binary by (Jeffries et al. 1995). We present here high resolution echelle spectroscopic observations of this binary, obtained during a 10 night run 12-21 January 1998 using the 2.1m telescope at McDonald Observatory. These observations reveal it is a double-lined spectroscopic binary. A dramatic increase in the chromospheric emissions (H_alpha and Ca II IRT lines) is detected during the observations. Several arguments favor the interpretation of this behavior as an unusual long-duration flare. First the temporal evolution of the event is similar to the observed in other solar and stellar flares, with an initial impulsive phase characterized by a strong increase in the chromospheric lines (the H_alpha EW change in a factor of 5 in only one day) and thereafter, the line emission decreased gradually over several days. Second, a broad component in the H_alpha line profile is observed just at the beginning of the event. Third, the detection of the He I D_{3} in emission and a filled-in He I 6678 A. We detect a Li I 6708 A line enhancement which is clearly related with the temporal evolution of the flare. The maximum Li I enhancement occurs just after the maximum chromospheric emission observed in the flare. We suggest that this Li I is produced by spallation reactions in the flare. This is the first time that such LiI enhancement associate with a stellar flare is reported, and probably the long-duration of this flare is a key factor for this detection.
As part of an All-Sky Automated Survey for SuperNovae (ASAS-SN) search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source, ASASSN-V J192114.84+624950.8, rapidly decreased in flux by $sim55%$ ($sim0.9$ mag) in the g-band. The textit{TESS} light curve revealed that the source is a highly eccentric, eclipsing binary. Fits to the light curve using textsc{phoebe} find the binary orbit to have $e=0.79$, $P_{rm orb}=18.462~text{days}$, and $i=88.6^{circ}$ and the ratios of the stellar radii and temperatures to be $R_2/R_1 = 0.71$ and $T_{e,2}/T_{e,1} = 0.82$. Both stars are chromospherically active, allowing us to determine their rotational periods of $P_1=1.52$ days and $P_2=1.79$ days, respectively. A LBT/MODS spectrum shows that the primary is a late-G or early-K type dwarf. Fits to the SED show that the luminosities and temperatures of the two stars are $L_1 = 0.48~L_{sun}$, $T_1= 5050~K$, $L_2 = 0.12~L_{sun}$, and $T_{2} = 4190~K$. We conclude that ASASSN-V J192114.84+624950.8 consists of two chromospherically active, rotational variable stars in a highly elliptical eclipsing orbit.
YZ Phe is a very short-period contact binary (Sp.= $K2,V$) with an orbital period of 0.2347 days near the short period limit (0.22 d). We present the complete light curves in $VRI$ bands, which photometric data were obtained with the 0.61-m telescope of PROMPT-8 at CTIO in Chile during June to October 2016 and August 2017. The photometric solutions were determined by using the W-D method and the results reveal that YZ Phe is a W-subtype shallow contact binary ($fsim$ 10%, $q$ = 2.635 or $1/q$ = 0.379 for W subtype) with rotational motion of a large hot spot on the more massive component, showing a strong OConnell effect with variation of maxima in photometric time series at period of 4.20 yr and stellar cycle at period of 1.28 yr. By compiling all available eclipse times, the result shows a long-term period decrease at a rate of $mathrm{d}P/mathrm{d}t = -2.64(pm 0.02)times 10^{-8}$ d $yr^{-1}$, superimposed on a cyclic variation ($A_3$ = 0.0081 days and $P_3$ = 40.76 years). This variation cannot be explained by Applegate mechanism. Thus, the cyclic change may be interpreted as light-travel time effect via the presence of a cool third body. Based on photometric solutions, the third light was detected with 2% contribution of total light in $V$ and $I$ bands. Those support the existence of a third body. For the long-term period decrease, it can be explained by mass transfer from the more massive component ($M_2 sim 0.74 M_{odot}$) to the less massive one ($M_1 sim 0.28 M_{odot}$) or plus AML via magnetic braking. With $1/q$ $<$ 0.4 and long-term period decrease, all suggest that YZ Phe is on the AML-controlled state and its fill-out factor will increase, as well as the system will evolve into a deeper normal contact binary.
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