High speed photometry in 2008 shows that the light curve of V842 Cen possesses a coherent modulation at 56.825 s, with sidebands at 56.598 s and 57.054 s. These have appeared since this nova remnant was observed in 2000 and 2002. We deduce that the dominant signal is the rotation period of the white dwarf primary and the sidebands are caused by reprocessing from a surface moving with an orbital period of 3.94 h. Thus V842 Cen is an intermediate polar (IP) of the DQ Herculis subclass, is the fastest rotating white dwarf among the IPs and is the third fastest known in a cataclysmic variable. As in other IPs we see no dwarf nova oscillations, but there are often quasi-periodic oscillations in the range 350 - 1500 s. There is a strong brightness modulation with a period of 3.78 h, which we attribute to negative superhumps, and there is an even stronger signal at 2.886 h which is of unknown origin but is probably a further example of that seen in GW Lib and some other systems. We used the Swift satellite to observe V842 Cen in the ultra-violet and in X-rays, although no periodic modulation was detected in the short observations. The X-ray luminosity of this object appears to be much lower than that of other IPs in which the accretion region is directly visible.
Even among the brigher cataclysmic variables an appreciable number of objects exist about which not much is known. One of them, MU Cen, was observed as part of a small project to better characterize these neglected systems. The temporal variations of the brightness of MU Cen during quiescence were studied in order to find clues to the structure of the system and its behaviour on time scales of hours and shorter. Light curves observed in white light at a time resolution of a few seconds and with a duration of several hours, obtained in six nights and spanning a total time base of five months, w…
The variable star V1129 Cen is classified in the GCVS as being of $β$ Lyr type. Unusual for such stars, it exhibits outbursts roughly once a year, lasting for $\sim$40 days. For this reason, a relationship to the dwarf novae has been suspected. Here, for the first time a detailed analysis of the light curve of the system is presented. Based on observations with high time resolution obtained at the Observatório do Pico dos Dias and on the long term ASAS light curve the orbital variations of the system are studied. They are dominated by ellipsoidal variations and partial eclipses of a probably s…
Fourteen years after its eruption as a classical nova (CN), V1047 Cen (Nova Cen 2005) began an unusual re-brightening in 2019 April. The amplitude of the brightening suggests that this is a dwarf nova (DN) eruption in a CN system. Very few CNe have had DN eruptions within decades of the main CN outburst. The 14 years separating the CN and DN eruptions of V1047 Cen is the shortest of all instances recorded thus far. Explaining this rapid succession of CN and DN outbursts in V1047 Cen may be challenging within the framework of standard theories for DN outbursts. Following a CN eruption, the mass…
Unique Nova Centauri 2005, V1047 Cen, by a form of the modified light curve was included into the CP Pup group. It means that the re-brightening in 2019 occurred still during the finishal stage of the 2005 outburst and can be connected with the current activity of the post-nova. The light curve of V1047 Cen in 2019 as a separate event is some details similar to the HR Del, Nova Del 1967, and also it is distinguish considerable from dwarf nova outbursts in post-nova systems (GK Per, etc.). There is proposed possible correct identification of Nova Sgr 1970, V3645 Sgr, which was included into the…
The Alpha Centauri system is the primary target for planet search as it is the closest star system composed of a solar twin Alpha Centauri A, a K-dwarf Alpha Centauri B and an M-dwarf Proxima Centauri, which has a confirmed planet in the temperate zone. Alpha Centauri A & B were monitored intensively with the HARPS spectrograph for over 10 years, providing high-precision radial velocity measurements. In this work we study the available data to better understand the stellar activity and other contaminating signals. We highlight the importance of telluric contamination and its impact on the radi…
We investigate retrieval of the stellar rotation signal for Proxima Centauri. We make use of high-resolution spectra taken with uves and harps of Proxima Centauri over a 13-year period as well as photometric observations of Proxima Centauri from asas and hst. We measure the Hα equivalent width and Hα index, skewness and kurtosis and introduce a method that investigates the symmetry of the line, the Peak Ratio, which appears to return better results than the other measurements. Our investigations return a most significant period of 82.6 $\pm$ 0.1 days, confirming earlier photometric results and…
Proxima and Alpha Centauri AB have almost identical distances and proper motions with respect to the Sun. Although the probability of such similar parameters is in principle very low, the question as to whether they actually form a single gravitationally bound triple system has been open since the discovery of Proxima one century ago. Owing to HARPS high precision absolute radial velocity measurements and the recent revision of the parameters of the Alpha Cen pair, we show that Proxima and Alpha Cen are gravitationally bound with a high degree of confidence. The orbital period of Proxima is ap…
The bright, nearby binary $α$ Centauri provides an excellent laboratory for testing stellar evolution models, as it is one of the few stellar systems for which we have high-precision classical (mass, radius, luminosity) and asteroseismic ($p$-mode) observations. Stellar models are created and fit to the classical and seismic observations of both stars by allowing for the free variation of convective mixing length parameter $α_{\text{MLT}}$. This system is modeled using five different sets of assumptions about the physics governing the stellar models. There are 31 pairs of tracks (out of ${\sim…
We present a study of white light flares from the active M5.5 dwarf Proxima Centauri using the Canadian microsatellite MOST. Using 37.6 days of monitoring data from 2014 and 2015, we have detected 66 individual flare events, the largest number of white light flares observed to date on Proxima Cen. Flare energies in our sample range from $10^{29}$-$10^{31.5}$ erg. The flare rate is lower than that of other classic flare stars of similar spectral type, such as UV Ceti, which may indicate Proxima Cen had a higher flare rate in its youth. Proxima Cen does have an unusually high flare rate given it…
The recent discovery of potentially habitable exoplanets around Proxima Centauri and TRAPPIST-1 has attracted much attention due to their potential for hosting life. We delineate a simple model that accurately describes the evolution of biological diversity on Earth. Combining this model with constraints on atmospheric erosion and the maximal evolutionary timescale arising from the star's lifetime, we arrive at two striking conclusions: (i) Earth-analogs orbiting low-mass M-dwarfs are unlikely to be inhabited, and (ii) K-dwarfs and some G-type stars are potentially capable of hosting more comp…
$α$ Centauri A is the closest solar-type star to the Sun and offers the best opportunity to find and ultimately to characterize an Earth-sized planet located in its Habitable Zone (HZ). Here we describe initial results from an ALMA program to search for planets in the $α$ Cen AB system using differential astrometry at millimeter wavelengths. Our initial results include new absolute astrometric measurements of the proper motion, orbital motion, and parallax of the $α$ Cen system. These lead to an improved knowledge of the physical properties of both $α$ Cen A and B. Our estimates of ALMA's rela…
$ω$ Centauri (NGC~5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of $ω$ Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete $J$ and $K_{\rm S}$ near-IR catalog of variable stars in the field of $ω$ Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the…
Brown dwarfs can serve as both clocks and chemical tracers of the evolutionary history of the Milky Way due to their continuous cooling and high sensitivity of spectra to composition. We focus on brown dwarfs in globular clusters that host some of the oldest coeval populations in the galaxy. Currently, no brown dwarfs in globular clusters have been confirmed, but they are expected to be uncovered with advanced observational facilities such as JWST. In this paper we present a new set of stellar models specifically designed to investigate low-mass stars and brown dwarfs in $ω$ Centauri -- the la…
The globular cluster Omega Centauri is the most massive and luminous cluster in the Galaxy. The $γ$-ray source FL8Y J1326.7$-$4729 is coincident with the core of the cluster, leading to speculation that hitherto unknown radio pulsars or annihilating dark matter may be present in the cluster core. Here we report on the discovery of five millisecond pulsars in Omega Centauri following observations with the Parkes radio telescope. Four of these pulsars are isolated with spin periods of 4.1, 4.2, 4.6 and 6.8 ms. The fifth has a spin period of 4.8 ms and is in an eclipsing binary system with an orb…
