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Register a new userSpectroscopic long-term monitoring of RZ Cas -- Part I: Basic stellar and system parameters
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H. Lehmann
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RZ Cas is a short-period Algol-type system showing episodes of mass transfer and Delta Sct-like oscillations of its mass-gaining primary component. We analyse high-resolution spectra of RZ Cas that we obtained during a spectroscopic long-term monitoring lasting from 2001 to 2017. Spectrum analysis resulted in precise atmospheric parameters of both components, in particular in surface abundances below solar values. We find that the variation of orbital period is semi-regular and derive different characteristic timescales for different epochs of observation. We show that the radial velocity variations with orbital phase can be modelled when including two cool spots on the surface of the secondary component. The modelling leads to precise masses and separation of the components. The seasonal variation of several parameters, such as vsin(i), rotation-orbit synchronisation factor, strength of the spots on the cool companion, and orbital period, can be characterised by a common timescale of the order of nine years. We interpret the timescale of nine years as the magnetic activity cycle of the cool companion. In particular the behaviour of the dark spots on the cool companion leads us to the interpretation that this timescale is based on an 18-year magnetic dynamo cycle. We conclude that the mass-transfer rate is controlled by the variable depth of the Wilson depression in the magnetic spot around the Lagrangian point L1. In the result, based on available data, we observe a damped activity cycle of the star, starting with a high mass-transfer episode around 2001, followed by quiet periods in 2006 and 2009, slightly higher activity around 2013 and 2014, and again followed by quiet periods in 2015 and 2016. However, owing to missing data for years 2010 and 2011, we cannot exclude that a second high mass-transfer episode occurred within this time span.
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We present results of a long-term spectroscopic monitoring program (since mid 2009) of Luminous Blue Variables with the new HERMES echelle spectrograph on the 1.2 m Mercator telescope at La Palma (Spain). We investigate high-resolution (R=80,000) optical spectra of two LBVs, P Cyg and HD 168607, the LBV candidates MWC 930 and HD 168625, and the LBV binary MWC 314. In P Cyg we observe flux changes in the violet wings of the Balmer H{alpha}, H{beta}, and He I lines between May and Sep 2009. The changes around 200 km/s to 300 km/s are caused by variable opacity at the base of the supersonic wind from the blue supergiant. We observe in MWC 314 broad double-peaked metal emission lines with invariable radial velocities over time. On the other hand, we measure in the photospheric S II {lambda}5647 absorption line, with lower excitation energy of ~14 eV, an increase of the heliocentric radial velocity centroid from 37 km/s to 70 km/s between 5 and 10 Sep 2009 (and 43 km/s on 6 Apr 2010). The increase of radial velocity of ~33 km/s in only 5 days can confirm the binary nature of this LBV close to the Eddington luminosity limit. A comparison with VLT-UVES and Keck-Hires spectra observed over the past 13 years reveals strong flux variability in the violet wing of the H{alpha} emission line of HD 168625, and in the absorption portion of the H{beta} line of HD 168607. In HD 168625 we observe H{alpha} wind absorption at velocities exceeding 200 km/s which develops between Apr and June 2010.
We present the results of a variability study of accreting young stellar objects in the Chameleon I star-forming region which is based on ~300 high resolution optical spectra from the multi-object fibre spectrograph FLAMES/GIRAFFE at the ESO/VLT. Twenty five objects with spectral types from G2-M5.75 were observed 12 times over the course of 15 months. Using the emission lines Ha (6562.81 A) and Ca II (8662.1 A) as accretion indicators we found 10 accreting and 15 non-accreting objects. We derived accretion rates for all accretors in the sample using the Ha equivalent width, Ha 10% width and the CaII equivalent width. The mean amplitude of variations in derived accretion rate from Ha equivalent width was ~ 0.37 dex, from Ca II equivalent width ~0.83 dex and from Ha 10% width ~1.11 dex. Based on the large amplitude of variations in accretion rates derived from the Ha 10% width with respect to the other diagnostics, we do not consider it to be a reliable accretion rate estimator. Taking the variations in Ha equivalent width and CaII equivalent width accretion rates to be closer to the true value, they suggest that the spread which has been found around the accretion rate to stellar mass relation is not due to the variability of individual objects on time-scales of weeks to ~1 year. From these variations we can also infer that the accretion rates are stable within < 0.37 dex over time-scales of less than 15 months. A major portion of the accretion variability was found to occur on less than the shortest time-scales in our observations, 8-25 days, which is comparable with the rotation periods of these young stellar objects. This could be an indication that what we are probing is spatial structure in the accretion flows, and also suggests that observations on time-scales of ~a couple of weeks are sufficient to limit the total extent of accretion rate variations in typical young stars.
We have spectroscopically monitored the galactic Luminous Blue Variable HD 160529 and obtained an extensive high-resolution data set that covers the years 1991 to 2002. During this period, the star evolved from an extended photometric minimum phase towards a new visual maximum. In several observing seasons, we covered up to four months with almost daily spectra. Our spectra typically cover most of the visual spectral range with a high spectral resolution (about 20,000 or more). This allows us to investigate the variability in many lines and on many time scales from days to years. We find a correlation between the photospheric HeI lines and the brightness of the star, both on a time scale of months and on a time scale of years. The short-term variations are smaller and do not follow the long-term trend, strongly suggesting different physical mechanisms. Metal lines also show both short-term and long-term variations in strength and also a long-term trend in radial velocity. Most of the line-profile variations can be attributed to changing strengths of lines. Propagating features in the line profiles are rarely observed. We find that the mass-loss rate of HD 160529 is almost independent of temperature, i.e. visual brightness.
The detection and subsequent characterisation of exoplanets are intimately linked to the characteristics of their host star. Therefore, it is necessary to study the star in detail in order to understand the formation history and characteristics of their companion(s). Our aims were to develop a community tool that allows the automated calculation of stellar parameters for a large number of stars, using high resolution echelle spectra and minimal photometric magnitudes, and introduce the first results in this work. We measured the equivalent widths of several iron lines and used them to solve the radiative transfer equation assuming local thermodynamic equilibrium to obtain the atmospheric parameters ($T_{text{eff}}$, [Fe/H], logg and $xi_t$). We used these values to derive the abundance of 11 chemical elements in the stellar photosphere (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Ni, Cu and Zn). Rotation and macroturbulent velocity were obtained using temperature calibrators and synthetic line profiles to match the observed spectra of five absorption lines. Finally, by interpolating in a grid of MIST isochrones, we derived the mass, radius and age using a Bayesian approach. SPECIES obtains bulk parameters that are in good agreement with measured values from different existing catalogues, including when different methods are used to derive them. We find excellent agreement with previous works that used similar methodologies. We find discrepancies in the chemical abundances for some elements with respect to other works, which could be produced by differences in $T_{text{eff}}$, or in the line list or the atomic line data used to derive them. We also obtained analytic relations to describe the correlations between different parameters, and we implemented new methods to better handle these correlations, which provides a better description of the uncertainties associated with the measurements.
The mode switching phenomenon of PSR B0329+54 is investigated based on the long-term monitoring from September 2003 to April 2009 made with the Urumqi 25m radio telescope at 1540 MHz. At that frequency, the change of relative intensity between the leading and trailing components is the predominant feature of mode switching. The intensity ratios between the leading and trailing components are measured for the individual profiles averaged over a few minutes. It is found that the ratios follow normal distributions, where the abnormal mode has a wider typical width than the normal mode, indicating that the abnormal mode is less stable than the normal mode. Our data show that 84.9% of the time for PSR B0329+54 was in the normal mode and 15.1% was in the abnormal mode. From the two passages of eight-day quasi-continuous observations in 2004, and supplemented by the daily data observed with 15 m telescope at 610 MHz at Jodrell Bank Observatory, the intrinsic distributions of mode timescales are constrained with the Bayesian inference method. It is found that the gamma distribution with the shape parameter slightly smaller than 1 is favored over the normal, lognormal and Pareto distributions. The optimal scale parameters of the gamma distribution is 31.5 minutes for the abnormal mode and 154 minutes for the normal mode. The shape parameters have very similar values, i.e. 0.75^{+0.22}_{-0.17} for the normal mode and 0.84^{+0.28}_{-0.22} for the abnormal mode, indicating the physical mechanisms in both modes may be the same. No long-term modulation of the relative intensity ratios was found for both the modes, suggesting that the mode switching was stable. The intrinsic timescale distributions, for the first time constrained for this pulsar, provide valuable information to understand the physics of mode switching.
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