We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, taken over multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis and VV Corona Australis. The stars in these 1-2" separation systems have optically thick circumstellar disks and high extinctions at optical and near-infrared wavelengths. Using a combination of new and archival data, we have determined the spectral types of all the stars in these two systems for the first time, examined the variable NIR veiling, measured the emission line equivalent widths, and created spectral energy distributions. They have similar spectral types (K7-M1) and are at approximately the same evolutionary stage, allowing comparison of the four stars in the two systems. We conclude that S CrA and VV CrA are young binary systems of stars bridging the Class I and Class II evolutionary stages, characterized by high accretion luminosities and variable emission lines.
Z Camelopardalis (Z Cam) stars are a subset of dwarf novae distinguished by the occurrence of standstills, periods of relative constant brightness one to one and a half magnitudes fainter than maximum brightness. As part of an ongoing observing campaign, the Z CamPaign, the authors focused attention on several Z Cam suspects in the southern hemisphere. Two stars, BP Coronae Australis and ST Chamaeleontis were found to exhibit standstill behavior in 2013, thus confirming them as Z Cam type systems. This adds two more bona fide members to the 19 confirmed Z Cams, bringing the total to 21.
Aims: Very Long Baseline Interferometry yields physical constraints on the compact radio emission of young stellar objects. At the same time, such measurements can be used for precise astrometric measurements of parallaxes and proper motions. Here, we aimed to make the first detections of very compact radio emission from class I protostars in the Corona Australis star-forming region. Methods: We have used the Long Baseline Array (LBA) to observe the protostars IRS 5 and IRS 7 in the Corona Australis star-forming region in three separate epochs Results: We report the first firm radio detection …
We combine published optical and near-infrared photometry to identify new low-mass candidate members in an area of about 0.64 deg^2 in Corona Australis, using the S-parameter method. Five new candidate members of the region are selected, with estimated ages between 3 and 15 Myr, and masses between 0.05 and 0.15 M_Sun. Using Spitzer photometry, we confirm that these objects are not surrounded by optically thick disks. However, one of them is found to display excess at 24 micron, thus suggesting it harbours a disk with an inner hole. With an estimated mass of 0.07 M_Sun according to the SED fitt…
We have performed a census of the young stellar populations near the Corona Australis molecular cloud using photometric and kinematic data from several sources, particularly Gaia EDR3, and spectroscopy of hundreds of candidate members. We have compiled a catalog of 393 members of Corona Australis, (39 at >M6), 293 (36) of which are spectroscopically classified for the first time in this work. We find that Corona Australis can be described in terms of two stellar populations, a younger one (few Myr) that is partially embedded in the cloud (the Coronet Cluster) and an older one (~15 Myr) that su…
We report JVLA 8-10 GHz ($λ$=3.0-3.7 cm) monitoring observations toward the YSO cluster R Coronae Australis (R\,CrA), taken in 2012, from March 15 to September 12. These observations were planned to measure the radio flux variabilities in timescales from 0.5 hours to several days, to tens of days, and up to $\sim$200 days. We found that among the YSOs detectable in individual epochs, in general, the most reddened objects in the \textit{Spitzer} observations show the highest mean 3.5 cm Stokes \textit{I} emission, and the lowest fractional variabilities on $<$200-day timescales. The brightest r…
Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photometric data set over a field of 128 deg$^{2}$ around the dark clouds of the region. We identify 313 high-probab…
The star S CrA is a tight visual binary consisting of two classical T Tauri stars, both with outstanding spectral characteristics and brightness variations. High-resolution spectra were collected at ESO and photometric observations with the SMARTS telescope. Both stars undergo large variation in brightness caused mainly by variable foreground extinction. From the stellar parameters we conclude that the two stars are remarkably similar, and that S CrA can be regarded as a T Tauri twin. Rotational periods and inclinations are also similar. The stars differ, however, in terms of degree of veiling…
The importance of the physical environment in the evolution of newly formed low-mass stars remains an open question. In particular, radiation from nearby more massive stars may affect both the physical and chemical structure of these kinds of young stars. Aims: To constrain the physical characteristics of a group of embedded low-mass protostars in Corona Australis in the vicinity of the young luminous Herbig Be star R CrA. Methods: Millimetre wavelength maps of molecular line and continuum emission towards the low-mass star forming region IRS7 near R CrA from the SMA and APEX are presented. Th…
We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2 field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from t…
We uncover the H2 flows in the Corona Australis molecular cloud and in particular identify the flows from the Coronet cluster. Near-infrared H2 v=1--0 S(1), 2.12micron-line, narrow-band imaging survey of the R CrA cloud core was carried out. We identify the best candidate-driving source for each outflow by comparing the flow properties, available proper motions, and the known/estimated properties of the driving sources. We also adopted the thumbrule of outflow power as proportional to source luminosity and inversely proportional to the source age to reach a consensus. Results: Continuum-subtra…
The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distri…
The ALMA Legacy survey of Class 0/I disks in Corona australis, Aquila, chaMaeleon, oPhiuchus north, Ophiuchus, Serpens (CAMPOS). I. Evolution of Protostellar disk radii
The late stages of evolution of the primordial circumstellar disks surrounding young stars are poorly understood, yet vital to constrain theories of planet formation. We consider basic structural models for the disks around two ~10 Myr-old members of the nearby RCrA association, RX J1842.9-3532 and RX J1852.3-3700. We present new arcsecond-resolution maps of their 230 GHz continuum emission from the Submillimeter Array and unresolved CO(3-2) spectra from the Atacama Submillimeter Telescope Experiment. By combining these data with broadband fluxes from the literature and infrared fluxes and spe…
Photoevaporation due to high-energy stellar photons is thought to be one of the main drivers of protoplanetary disk dispersal. The fully or partially ionized disk surface is expected to produce free-free continuum emission at centimeter (cm) wavelengths that can be routinely detected with interferometers such as the upgraded Very Large Array (VLA). We use deep (rms noise down to 8 $μ$Jy beam$^{-1}$ in the field of view center) 3.5 cm maps of the nearby (130 pc) Corona Australis (CrA) star formation (SF) region to constrain disk photoevaporation models. We find that the radio emission from disk…
To investigate the inner regions of protoplanetary disks, we performed near-infrared interferometric observations of the classical TTauri binary system S CrA. We present the first VLTI-GRAVITY high spectral resolution ($R\sim$4000) observations of a classical TTauri binary, S CrA (composed of S CrA N and S CrA S and separated by $\sim$1.4"), combining the four 8-m telescopes in dual-field mode. Our observations in the near-infrared K-band continuum reveal a disk around each binary component, with similar half-flux radii of about 0.1 au at d$\sim$130 pc, inclinations ($i=$28$\pm$3$^o$\ and $i=$…
The CrA region and the Coronet cluster form a nearby (138 pc), young (1-2 Myr) star-forming region hosting a moderate population of YSO. We present Herschel PACS photometry at 100 and 160 micron, obtained as part of the Herschel Gould Belt Survey. The Herschel maps reveal the cluster members with high sensitivity and high dynamic range. Many of the cluster members are detected, including some embedded, very low-mass objects, several protostars, and substantial emission from the surrounding cloud. The Herschel data provide sufficient spatial resolution to detect small-scale details, such as bri…
In recent years, the disk populations in a number of young star-forming regions have been surveyed with ALMA. Understanding the disk properties and their correlation with those of the central star is critical to understand planet formation. In particular, a decrease of the average measured disk dust mass with the age of the region has been observed. We conducted high-sensitivity continuum ALMA observations of 43 Class II young stellar objects in CrA at 1.3 mm (230 GHz). The typical spatial resolution is 0.3". The continuum fluxes are used to estimate the dust masses of the disks, and a surviva…
We present potential detections of H-band scattered light emission around four young star, selected from a total sample of 45 young stars observed with the CIAO coronagraph of the Subaru telescope. Two CTTS, CI Tau and DI Cep, and two WTTS, LkCa 14 and RXJ 0338.3+1020 were detected. In all four cases, the extended emission is within the area of the residual PSF halo, and is revealed only through careful data reduction. We compare the observed extended emission with simulations of the scattered light emission, to evaluate the plausibility and nature of the detected emission.
In our own solar system, the necessity of understanding space weather is readily evident. Fortunately for Earth, our nearest stellar neighbor is relatively quiet, exhibiting activity levels several orders of magnitude lower than young, solar-type stars. In protoplanetary systems, stellar magnetic phenomena observed are analogous to the solar case, but dramatically enhanced on all physical scales: bigger, more energetic, more frequent. While coronal mass ejections (CMEs) could play a significant role in the evolution of protoplanets, they could also affect the evolution of the central star itse…
The X-ray satellite XMM-Newton has so far revealed coronal cycles in seven solar-like stars. In this sample, the youngest stars $ε$ Eridani (400 Myr) and $ι$ Horologii (600 Myr) display the shortest X-ray cycles and the smallest cycle amplitudes. The corona of $ε$ Eridani was modelled in terms of solar magnetic structures (active regions, cores of active regions and flares) at varying filling factors. The study revealed that 65-95% of its corona is covered with magnetic structures, and this was held responsible for the low X-ray cycle amplitude. It was also hypothesized that the basal surface …
Theta 1 Ori E is a young, moderate mass binary system, a rarely observed case of spectral-type G-giants of about 3 Solar masses, which are still collapsing towards the main sequence. We have obtained high resolution X-ray spectra with Chandra and find that the system is very active and similar to coronal sources, having emission typical of magnetically confined plasma: a broad temperature distribution with a hot component and significant high energy continuum; narrow emission lines from H- and He-like ions, as well as a range of Fe ions, and relative luminosity, L_x/L_bol = 0.001. Density, whi…
Above the top of the solar corona, the young slow solar wind transitions from low-beta, magnetically structured flow dominated by radial structures, to high-beta, less structured flow dominated by hydrodynamics. This transition, long inferred via theory, is readily apparent in the sky region close to 10 degrees from the Sun, in processed, background-subtracted solar wind images. We present image sequences collected by the STEREO/HI1 instrument in 2008 Dec, covering apparent distances from approximately 4 to 24 degrees from the center of the Sun and spanning this transition in large-scale morph…
The young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of X-ray and Extreme UV (EUV) flux, stellar wind and eruptive events. These outputs are the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. While X-ray fluxes and surface magnetic fields can be derived from observations, the EUV emission and wind mass fluxes, Coronal Mass Ejections and associated Stellar Energetic Particle events cannot be directly observed. Here, we present the results of a three-dimensional magnetohydrodynamic (MHD) model …
Energetic flares and associated coronal mass ejections (CMEs) from young magnetically active solar-like stars can play a critical role in setting conditions for atmospheric escape as well aspenetration of accelerated particles into their atmospheres that promotes formation of biologically relevant molecules. We have used the observationally reconstructed magnetic field of the 0.7 Gyr-young Suns twin, k1 Ceti, to study the effects of CME deflections in the magnetic corona of the young Sun and their effects on the impact frequency on the early Venus, Earth and Mars. We find that the coronal magn…
BANYAN $Σ$ is a new Bayesian algorithm to identify members of young stellar associations within 150 pc of the Sun. It includes 27 young associations with ages in the range ~1-800 Myr, modelled with multivariate Gaussians in 6-dimensional XYZUVW space. It is the first such multi-association classification tool to include the nearest sub-groups of the Sco-Cen OB star-forming region, the IC 2602, IC 2391, Pleiades and Platais 8 clusters, and the $ρ$ Ophiuchi, Corona Australis, and Taurus star-formation regions. A model of field stars is built from a mixture of multivariate Gaussians based on the …
Aims. R Coronae Australis (R CrA) is the brightest star of the Coronet nebula of the Corona Australis (CrA) star forming region. It has very red colors, probably due to dust absorption and it is strongly variable. High contrast instruments allow for an unprecedented direct exploration of the immediate circumstellar environment of this star. Methods. We observed R CrA with the near-IR channels (IFS and IRDIS) of SPHERE at VLT. In this paper, we used four different epochs, three of them from open time observations while one is from the SPHERE guaranteed time. The data were reduced using the DRH …
This article summarizes the processes of high-energy emission in young stellar objects. Stars of spectral type A and B are called Herbig Ae/Be (HAeBe) stars in this stage, all later spectral types are termed classical T Tauri stars (CTTS). Both types are studied by high-resolution X-ray and UV spectroscopy and modeling. Three mechanisms contribute to the high-energy emission from CTTS: 1) CTTS have active coronae similar to main-sequence stars, 2) the accreted material passes through an accretion shock at the stellar surface, which heats it to a few MK, and 3) some CTTS drive powerful outflows…
In this paper we present chromospheric emission levels of the solar-type stars in the young open clusters IC 2391 and IC 2602. High resolution spectroscopic data were obtained for over 50 F, G, and K stars from these clusters over several observing campaigns using the University College London Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Unlike older clusters, the majority (28/52) of the solar-type stars in the two clusters are rapid-rotators (vsini > 20 km/s) with five of the stars being classified as ultra-rapid rotators (vsini > 100 km/s). The emission levels in the Calcium…
Young stars show a variety of highly energetic phenomena, from accretion and outflow processes to hot coronal plasmas confined in their outer atmosphere, all regulated by the intense stellar magnetic fields. Many aspects on each of these phenomena are debated, but, most notably, their complex mutual interaction remains obscure. In this work I report how these phenomena are simultaneously responsible for the high-energy emission from young stars, with a special focus on the expected and observed variability in the X-ray band. Investigating variations in the X-ray emission from young stars allow…
Throughout an activity cycle, magnetic structures rise to the stellar surface, evolve and decay. Tracing their evolution on a stellar corona allows us to characterize the X-ray cycles. However, directly mapping magnetic structures is feasible only for the Sun, while such structures are spatially unresolved with present-day X-ray instruments on stellar coronae. We present here a new method, implemented by us, that indirectly reproduces the stellar X-ray spectrum and its variability with solar magnetic structures. The technique converts solar corona observations into a format identical to that o…
We analyze the X-ray spectra of the $\sim$8000 sources detected in the Cygnus OB2 Chandra Legacy Survey (Drake et al., this issue), with the goals of characterizing the coronal plasma of the young low-mass stars in the region and estimating their intrinsic X-ray luminosities. We adopt two different strategies for X-ray sources for which more or less than 20 photons were detected. For the brighter sample we fit the spectra with absorbed isothermal models. In order to limit uncertainties, for most of the fainter Cygnus OB2 members in this sample, we constrain the spectral parameters to character…
We present an analysis of the high-resolution Chandra observation of the multiple system, HD 155555 (an RS CVn type binary system, HD 155555 AB, and its spatially resolved low-mass companion HD 155555 C). This is an intriguing system which shows properties of both an active pre-main sequence star and a synchronised (main sequence) binary. We obtain the emission measure distribution, temperature structures, plasma densities, and abundances of this system and compare them with the coronal properties of other young/active stars. HD 155555 AB and HD 155555 C produce copious X-ray emission with log…
The 9 Myr old TW Hya Association (TWA) is the nearest group (typical distances of $\sim$50 pc) of pre-main-sequence (PMS) stars with ages less than 10 Myr and contains stars with both actively accreting disks and debris disks. We have studied the coronal X-ray emission from a group of low mass TWA common proper motion binaries using the {\it{Chandra}} and {\it{Swift}} satellites. Our aim is to understand better their coronal properties and how high energy photons affect the conditions around young stars and their role in photo-exciting atoms, molecules and dust grains in circumstellar disks an…
Coronal Mass Ejections from Young Suns: Insights from Solar and Stellar Observations and Models
NASA Goddard Space Flight Center（NASA戈达德太空飞行中心）；The Catholic University of America（美国天主教大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学Hakubi高级研究中心）；Department of Physics, Kyoto University（京都大学物理系）
Context: The shortest chromospheric (Ca II H&K) activity cycle (1.6 yr) has been recently discovered in the young (~600 Myr) solar-like star iota Hor. Coronal X-ray activity cycles have only been discovered in a few stars other than the Sun, all of them with an older age and a lower activity level than iota Hor. Aims: We intended to find the X-ray coronal counterpart of the chromospheric cycle for i Hor. This represents the first X-ray cycle observed in an active star, as well as the paradigm of the first coronal cycles in the life of a solar-like star. Methods: We monitored i Hor with XMM-New…
Chromospheric activity cycles are common in late-type stars; however, only a handful of coronal activity cycles have been discovered. \ihor\ is the most active and youngest star with known coronal cycles. It is also a young solar analog, and we are likely facing the earliest cycles in the evolution of solar-like stars, at an age (~600 Myr) when life appeared on Earth. Our aim is to confirm the ~1.6 yr coronal cycle and characterize its stability over time. We use X-ray observations of iota Hor to study the corona of a star representing the solar past through variability, thermal structure, and…
Many neutron stars (NSs) and runaway stars apparently come from the same regions on the sky. This suggests that they share the same birth places, namely associations and clusters of young massive stars. To identify NS birth places, we attempt to and NS-runaway pairs that could be former companions that were disrupted in a supernova (SN). The remains of recent (<few Myr) nearby (< 150 pc) SNe should still be identifiable by observing the emission of rare radioisotopes such as 26Al and 60Fe that can also be used as additional indicators to confirm a possible SN event. We investigated the origin …
We analyzed X-Shooter/VLT spectra of 24 ClassIII sources from three nearby star-forming regions (sigmaOrionis, LupusIII, and TWHya). We determined the effective temperature, surface gravity, rotational velocity, and radial velocity by comparing the observed spectra with synthetic BT-Settl model spectra. We investigated in detail the emission lines emerging from the stellar chromospheres and combined these data with archival X-ray data to allow for a comparison between chromospheric and coronal emissions. Both X-ray and Halpha luminosity as measured in terms of the bolometric luminosity are ind…
We conducted a near-infrared imaging survey of 11 young dwarfs in the Pleiades cluster using the Subaru Telescope and the near-infrared coronagraph imager. We found 10 faint point sources, with magnitudes as faint as 20 mag in the K-band, around 7 dwarfs. Comparison with Spitzer archive images revealed that a pair of the faint sources around V 1171 Tau are very red in the infrared wavelengths, indicative of very low-mass young stellar objects. However, the results of our follow-up proper motion measurements implied that the central star and the faint sources do not share common proper motions,…
The diagram of indices of coronal and chromospheric activity allowed us to reveal stars where solar-type activity appears and regular cycles are forming. Using new consideration of a relation between coronal activity and the rotation rate, together with new data on the ages of open clusters, we estimate the age of the young Sun corresponding to the epoch of formation of its cycle. The properties of the activity of this young Sun, with an age slightly older than one billion years, are briefly discussed. An analysis of available data on the long-term regular variability of late-type stars leads …
We study the dependence of the coronal activity index on the star's rotation rate. This question was considered earlier for 824 late-type stars on the basis of a consolidated catalogue of the soft X-ray fluxes. We carry out a more refined analysis separately for G, K and M dwarfs. They distinctively exhibit two modes of activity. The first one is the saturation mode, it is characteristic of young stars and is practically not related to their rotation. The second one refers to the solar-type activity the level of which strongly depends on the rotation period. We show that the transition from on…
Young and rapidly rotating stars are known for intense, dynamo generated magnetic fields. Spectropolarimetric observations of those stars in precisely aged clusters are key input for gyrochronology and magnetochronology. We use ZDI maps of several young K-type stars of similar mass and radius but with various ages and rotational periods, to perform 3D numerical MHD simulations of their coronae and follow the evolution of their magnetic properties with age. Those simulations yield the coronal structure as well as the instant torque exerted by the magnetized, rotating wind on the star. As stars …
Young and magnetically active low-mass stars often exhibit non-thermal coronal radio emission due to the gyration of electrons in their magnetized chromospheres. This emission is easily detectable at centimeter wavelengths with the current sensitivity of large radio interferometers like the VLA. With the aim of identifying nearby stars adequate for future accurate radio astrometric monitoring using Very Long Baseline Interferometry (VLBI), we have used the VLA in its B\, configuration to search for radio emission at \mbox{$ν\simeq 6$\,GHz} \mbox{($λ\simeq 5$\,cm)} toward a sample of 170 nearby…
Classical T Tauri stars (CTTS) differ in their X-ray signatures from older pre-main sequence stars, e.g. weak-lined TTS (WTTS). CTTS show a soft excess and deviations from the low-density coronal limit in the He-like triplets. We test whether these features correlate with accretion or the presence of a disk by observing IM Lup, a disk-bearing object apparently in transition between CTTS and WTTS without obvious accretion. We analyse a Chandra grating spectrum and additional XMM-Newton data of IM Lup and accompanying optical spectra, some of them taken simultaneously to the X-ray observations. …
Coronal Mass Ejections from Young Suns: An Observational View through the Solar-Stellar Connection
The Hakubi Center for Advanced Research, Kyoto University（京都大学白兔高级研究中心）；Department of Physics, Kyoto University（京都大学物理系）；Heliophysics Science Division, NASA Goddard Space Flight Center（NASA戈达德太空飞行中心太阳物理学部）；Department of Physics, The Catholic University of America（美国天主教大学物理系）
We report the detection of multiple quasi-periodic pulsations (QPPs) observed during the flaring activity of KIC 8414845, a young, active solar-type star observed by the Kepler mission launched by NASA. We analyzed the QQP signal using a data-driven, nonparametric method called singular spectrum analysis (SSA), which has never been utilized previously for analyzing solar or stellar QPPs. Because it is not based on a prescribed choice of basis functions, SSA is particularly suitable for analyzing nonstationary, nonlinear signals such as those observed in QPPs during major flares. The analysis h…
A fine analysis of spectral line widths and Doppler shifts employing Fourier transform and cross-correlation techniques has been applied to Chandra HETG spectra obtained in 1999 October of the rapidly rotating young star AB Doradus in order to investigate its coronal topology. The observation lasted 52.3ks, covering 1.2 rotation periods. The X-ray light curve obtained from integrating the dispersed signal revealed a moderate intensity flare midway through the exposure in which the count rate increased sharply by about 50% and subsequently decayed over the next 10ks. We find no significant Dopp…
The Chandra High Energy Transmission Gratings (HETG) Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster which provides high resolution X-ray spectra of very young stars over a wide mass range (0.7 - 2.3 Msun). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts which are well-characterized at optical and infra-red wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction indicating that the sources are located on the near side of the …
