Pre-main Sequence Research Articles

Photometric determination of the mass accretion rates of pre-main-sequence stars

We studied the properties of the young stellar populations in the NGC 299 cluster in the Small Magellanic Cloud using observations obtained with the Hubble Space Telescope in the V, I, and Hα bands. We identified 250 stars with Hα excess exceeding 5σ and an equivalent width of the Hα emission line of at least 20 Å, which indicates that these stars are still undergoing active accretion and therefore represent bona fide pre-main-sequence (PMS) objects. For 240 of them, we derived physical stellar parameters such as the mass, age, and mass accretion rate by comparing the observed photometry with theoretical models. We find evidence that suggests the existence of two populations of PMS stars, one with a median age of around 25 Myr and the other about 50 Myr old. These ages are consistent with previously determined ages for the main population of the cluster. The average mass accretion rate for these PMS stars is ∼5 × 10−9 M⊙ yr−1, which is comparable to the values found with the same method in other low-metallicity, low-density clusters in the Magellanic Clouds, but is about a factor of three lower than those measured for stars of similar mass and age in denser Magellanic Cloud stellar regions. Our findings support the hypothesis that both the metallicity and density of the forming environment can affect the mass accretion rate and thus the star formation process in a region. A study of the spatial distribution of both massive stars and (low-mass) PMS objects reveals that the former are clustered near the nominal centre of NGC 299, whereas the PMS stars are rather uniformly distributed over the field. Although it is possible that the PMS stars formed in situ in a more diffuse manner than massive stars, it is also plausible that the PMS stars formed initially in a more compact structure together with the massive stars and were later dispersed due to two-body relaxation. To explore this possibility, we studied the cluster’s stellar density profile. We find a core radius rc ≃ 0.6 pc and a tidal radius rt ≃ 5.5 pc, with an implied concentration parameter c ≃ 1, suggesting that the cluster could be dispersing into the field.

Photometric determination of the mass accretion rates of pre-main-sequence stars

Aims. We study the properties of low-mass stars recently formed in the field of the NGC 376 cluster in the Small Magellanic Cloud (SMC). Methods. Using photometric observations acquired with the Hubble Space Telescope (HST) in the V, I, and Hα bands, we identify 244 candidate pre-main-sequence (PMS) stars showing Hα excess emission at the 5σ level and with Hα equivalent width of 20 Å or more. We derive physical parameters for all PMS stars, including masses, ages, and mass accretion rates. We compare the effective mass accretion rate of stars in NGC 376 to that of objects in the NGC 346 cluster, with NGC 346 featuring similar metallicity but higher total mass and gas density. Results. We find a median age of 28 Myr for this population (with 25th and 75th percentiles at about 20 and 40 Myr, respectively), in excellent agreement with previous studies of massive stars in the same field. The PMS stars are rather uniformly distributed across the field, whereas massive stars are more clustered. The spatial distribution of PMS objects is compatible with them having formed in the centre of the cluster and then migrating outwards. We find that in NGC 376 the mass accretion rate is systematically lower than in NGC 346 for stars of the same mass and age. This indicates that, in addition to metallicity, there are other environmental factors affecting the rate of mass accretion onto PMS stars. Our observations suggest that the gas density in the star-forming region might play a role.

Implications of Atmospheric Nondetections for Trappist-1 Inner Planets on Atmospheric Retention Prospects for Outer Planets

JWST secondary eclipse observations of Trappist-1b seemingly disfavor atmospheres >∼1 bar since heat redistribution is expected to yield dayside emission temperature below the ∼500 K observed. Given the similar densities of Trappist-1 planets, and the theoretical potential for atmospheric erosion around late M dwarfs, this observation might be assumed to imply substantial atmospheres are also unlikely for the outer planets. However, the processes governing atmosphere erosion and replenishment are fundamentally different for inner and outer planets. Here, an atmosphere–interior evolution model is used to show that an airless Trappist-1b (and c) only weakly constrains stellar evolution, and that the odds of outer planets e and f retaining substantial atmospheres remain largely unchanged. This is true even if the initial volatile inventories of planets in the Trappist-1 system are highly correlated. The reason for this result is that b and c sit unambiguously interior to the runaway greenhouse limit, and so have potentially experienced ∼8 Gyr of X-ray and extreme ultraviolet–driven hydrodynamic escape; complete atmospheric erosion in this environment only weakly constrains stellar evolution and escape parameterizations. In contrast, e and f reside within the habitable zone, and likely experienced a comparatively short steam atmosphere during Trappist-1's pre-main sequence, and consequently complete atmospheric erosion remains unlikely across a broad swath of parameter space (e and f retain atmospheres in ∼98% of model runs). Naturally, it is still possible that all Trappist-1 planets formed volatile-poor and are all airless today. But the airlessness of b (and c) does not require this, and as such, JWST transit spectroscopy of e and f remains the best near-term opportunity to characterize the atmospheres of habitable zone terrestrial planets.

The star in RNO 54: A possible post-FUor with a short faint jet

Aims. The aim of the present study is to analyze the spectra of an unusual pre-main sequence star in the cometary nebula RNO 54, which is suspected by several researchers to be a FUori-like object. Methods. We performed long-slit spectroscopy of the star using the 6m telescope with the SCORPIO-2 multi-mode focal reducer. Results. We discover a short (~4″ or ~6000 AU) and faint emission shock-excited jet from this star, probably oriented toward the long axis of the nebular ellipse. The spectral type of the star is estimated as G0-2 II; we confirm the split of the Li I absorption line, which is a typical sign indicating a FUori-like spectrum. Our analysis of the available data reveals an almost null photometric variability over at least the last 20 years. The lower limit of the bolometric luminosity of the star is estimated as 300 L⊙. Our study supports the classification of RNO 54 as a FUor-like star in the long post-outburst stage.

Time-series photometry and multiwavelength characterization of the young stellar cluster Mon R2

ABSTRACT Using the Las Cumbres Observatory Global Telescope Network (LCOGT), we have obtained multi-epoch photometry of the young cluster Mon R2. We have monitored over 6000 sources with i-band between 13 and 23 mag within a 26 × 26 arcmin2 field of view. For each star, we collected ∼1500 photometric points covering a temporal window of 23 d. Based on these data, we have measured rotation-modulated of 136 stars and identified around 90 additional variables, including 14 eclipsing binary candidates. Moreover, we found 298 other variables with photometric high-scatter. In addition, we have obtained r-band and Hα narrow-band photometry of the cluster with LCOGT and low-resolution optical spectroscopy of 229 stars with GMOS-Gemini. We used the Gaia data from the periodic stars and objects with Hα or IR-excesses, which are mostly low-mass pre-main sequence stars (<1 M⊙) in the cluster to estimate the distance (825 ± 51 pc) and the mean proper motions (μαcos(δ) = −2.75 mas yr−1 and μδ = 1.15 mas yr−1) of its members. This allows us to use the Gaia data to identify additional Mon R2 member candidates. We also used Pan-STARRS photometry from our LCOGT sources to construct a more precise H-R diagram, from which we estimate the mean age of the cluster and identify other possible members including eleven spectroscopy brown dwarf with M7 to M9 GMOS spectral types. Finally, we combined our membership lists with Spitzer infrared photometry to investigate the incidence of stars with discs and the effect these have on stellar rotation.

Stellar Rotation and Structure of the α Persei Complex: When Does Gyrochronology Start to Work?

On the pre-main sequence, the rotation rates of Sun-like stars are dictated by the interplay between the protostellar disk and the star’s contraction. At ages exceeding 100 Myr, magnetic spindown erases the initial stellar spin rate and enables rotation-based age dating (gyrochronology). The exact time at which the transition between these two regimes occurs depends on stellar mass, and has been challenging to empirically resolve due to a lack of viable calibration clusters. The α Persei open cluster (t ≈ 80 Myr, d ≈ 170 pc) may provide the needed calibrator, but recent analyses of the Gaia data have provided wildly varying views of its age and spatial extent. As such, we analyze a combination of TESS, Gaia, and LAMOST data to calibrate gyrochronology at the age of α Per and to uncover the cluster’s true morphology. By assembling a list of rotationally confirmed α Per members, we provide strong evidence that α Per is part of a larger complex of similarly aged stars. Through kinematic back-integration, we show that the most diffuse components of α Per were five times closer together 50 Myr ago. Finally, we use our stellar rotation periods to derive a relative gyrochronology age for α Per of 67% ± 12% the age of the Pleiades, which yields 86 ± 16 Myr given current knowledge. We show that by this age, stars more massive than ≈0.8 M ⊙ have converged to form a well-defined slow sequence.

Theoretical tidal evolution constants for stellar models from the pre-main sequence to the white dwarf stage

Aims. One of the most reliable means of studying the stellar interior is through the apsidal motion in double line eclipsing binary systems since these systems present errors in masses, radii, and effective temperatures of only a few per cent. On the other hand, the theoretical values of the apsidal motion to be compared with the observed values depend on the stellar masses of the components and more strongly on their radii (fifth power). The main objective of this work is to make available grids of evolutionary stellar models that, in addition to the traditional parameters (e.g. age, mass, log g, Teff), also contain the necessary parameters for the theoretical study of apsidal motion and tidal evolution. This information is useful for the study of the apsidal motion in eclipsing binaries and their tidal evolution, and can also be used for the same purpose in exoplanetary systems. Methods. All models were computed using the MESA package. We consider core overshooting for models with masses ≥1.2M⊙. For the amount of core overshooting we adopted a recent relationship for mass × core overshooting. We adopted for the mixing-length parameter αMLT the value 1.84 (the solar-calibrated value). Mass loss was taken into account in two evolutionary phases. The models were followed from the pre-main sequence phase to the white dwarf (WD) stage. Results. The evolutionary models containing age, luminosity, log g, and Teff, as well as the first three harmonics of the internal stellar structure (k2, k3, and k4), the radius of gyration βy, and the dimensionless variable α, related to gravitational potential energy, are presented in 69 tables covering three chemical compositions: [Fe/H] = −0.50, 0.00, and 0.50. Additional models with different input physics are available.

Gaia Data Release 3

Context. The Gaia Radial Velocity Spectrometer (RVS) provides the unique opportunity of a spectroscopic analysis of millions of stars at medium resolution (λ/Δλ ∼ 11 500) in the near-infrared (845−872 nm). This wavelength range includes the Ca II infrared triplet (IRT) at 850.03, 854.44, and 866.45 nm, which is a good indicator of magnetic activity in the chromosphere of late–type stars. Aims. Here we present the method devised for inferring the Gaia stellar activity index from the analysis of the Ca II IRT in the RVS spectrum, together with its scientific validation. Methods. The Gaia stellar activity index is derived from the Ca II IRT excess equivalent width with respect to a reference spectrum, taking the projected rotational velocity (vsini) into account. We performed scientific validation of the Gaia stellar activity index by deriving a R′IRT index, which is largely independent of the photospheric parameters, and considering the correlation with the R′HK index for a sample of stars. A sample of well-studied pre-main-sequence (PMS) stars is considered to identify the regime in which the Gaia stellar activity index may be affected by mass accretion. The position of these stars in the colour–magnitude diagram and the correlation with the amplitude of the photometric rotational modulation is also scrutinised. Results.Gaia DR3 contains a stellar activity index derived from the Ca II IRT for some 2 × 106 stars in the Galaxy. This represents a ‘gold mine’ for studies on stellar magnetic activity and mass accretion in the solar vicinity. Three regimes of the chromospheric stellar activity are identified, confirming suggestions made by previous authors based on much smaller R′HK datasets. The highest stellar activity regime is associated with PMS stars and RS CVn systems, in which activity is enhanced by tidal interaction. Some evidence of a bimodal distribution in main sequence (MS) stars with Teff ≳ 5000 K is also found, which defines the two other regimes, without a clear gap in between. Stars with 3500 K ≲ Teff ≲ 5000 K are found to be either very active PMS stars or active MS stars with a unimodal distribution in chromospheric activity. A dramatic change in the activity distribution is found for Teff ≲ 3500 K, with a dominance of low activity stars close to the transition between partially- and fully convective stars and a rise in activity down into the fully convective regime.

The Effelsberg survey of FU Orionis and EX Lupi objects

Context. FU Orionis (FUor) and EX Lupi (EXor) type objects are two groups of peculiar and rare pre-main sequence low-mass stars that are undergoing powerful accretion outbursts during their early stellar evolution. Although water masers are widespread in star-forming regions and serve as powerful probes of mass accretion and ejection on small scales, little is known about the prevalence of water masers toward FUors and EXors. Aims. We aim to perform the first systematic search for the 22.2 GHz water maser line in FUors and EXors in order to determine its overall incidence in these eruptive variables and to facilitate high angular-resolution follow-up observations. Methods. We used the Effelsberg 100-m radio telescope to observe the H2O (616 – 523) transition at 22.2GHz toward a sample of 51 eruptive young stellar objects. Results. We detected a total of five water masers in our survey; three are associated with eruptive stars, equivalent to a detection rate of ~6% for our sample of eruptive sources. These detections include one EXor, V512 Per (also known as SVS 13 or SVS 13A), and two FUors, Z CMa, and HH 354 IRS. This is the first reported detection of water maser emission towards HH 354 IRS. We also detected water maser emission in our pointing towards the FUor binary RNO 1B/1C, which most likely originates from the nearby deeply embedded source IRAS 00338+6312 (~4″ from RNO 1B/1C). Emission was also detected from H2O(B), (also known as SVS 13C), a Class 0 source ~30″ from the EXor V512 Per. The peak flux density of H2O(B) in our observations, 498.7 Jy, is the highest observed to date, indicating that we have serendipitously detected a water maser flare in this source. In addition to the two non-eruptive Class 0 sources (IRAS 00338+6312 and H2O(B)/SVS 13C), we detected maser emission towards one Class 0/I (HH 354 IRS) and two Class I (V512 Per/SVS 13A and Z CMa) eruptive stars. Conclusions. Despite the low detection rate, we demonstrate the presence of 22.2 GHz water maser emission in both FUor and EXor systems, paving the way to radio interferometric observations to study the environments of these eruptive stars on small scales. Comparisons of our data with historical observations spanning several decades suggest that multiple water maser flares have occurred in both V512 Per and H2O(B).

Pre-Main Sequence Ap Star LkHα 324/B in LDN 988 Star Forming Region

We present results of the investigation of the star LkHα 324/B, which belongs to the starforming dark cloud LDN 988. Based on high resolution spectroscopy, we determined its fundamental parameters as Teff=11,175±130 K, log(L*/L⊙)=1.87±0.07. According to these parameters, we found that LkHα 324/B is a pre-main sequence star with mass M≈3M⊙ and age t≈2.9 Myr. Recently, it underwent the phase of actively accreting the Herbig Ae/Be star, but accretion has now ceased in the LkHα 324/B system. This is consistent with the fact that the star is surrounded by a circumstellar disk with an inner cavity, as was determined from its spectral energy distribution. Our analysis revealed the peculiar abundance pattern of LkHα 324/B typical to those of magnetic Ap stars. It possesses mild underabundance of the light elements and excess up to ∼2–4 dex (in comparison to the Sun) of the iron peak and rare earth elements. We found no evidence for abrupt vertical abundances gradients in the lines forming the region of the LkHα 324/B atmosphere, in agreement with the results of the theoretical diffusion calculations in this temperature domain. From the intensification of the magnetically sensitive lines, we deduced that LkHα 324/B probably hosts a global magnetic field of ⟨B⟩≈3.5 kG strength. We suppose that the stabilizing role of this field favored the elements’ separation by diffusion before the star reached the main sequence.

Magneto-convective Modeling of Low-mass Pre-main Sequence Stars: Postponing the Depletion of Lithium

Standard evolutionary models of pre-main sequence (PMS) low-mass stars often predict radii R and Li abundances A(7Li) which are too small to agree with empirical data, while effective temperatures T eff are predicted to be too large. There are also discrepancies in replicating the stellar age. Discrepancies in R, T eff, and A(7Li) are reported by Stassun et al. for both components (A/B) of the eclipsing binary 2M1222-57 belonging to the young Lower Centaurus Crux association. Using the output of a magneto-convective stellar evolution model which we applied in an early study (in 2010) of PMS stars in a different young association, we show that the discrepancies reported by Stassun et al. in the 2M1222-57 system are alleviated. The models are instructive in showing why larger lithium abundances occur in magnetic PMS stars: it takes longer for the central gas in such a star to become hot enough to destroy lithium.

Magnetospheric accretion at the late phases of the pre-main-sequence evolution: the case of RZ Psc

ABSTRACT It has been shown that during the burst of accretion activity observed in UX Ori-type star RZ Psc in 2013, the accretion rate increased approximately by an order of magnitude. This means that the accretion process at the late stages of the pre-main sequence evolution is very unstable. Using the spectra obtained during this episode, we have studied the magnetospheric emission in the H α line. Models of magnetospheric accretion are calculated to obtain the parameters of the magnetosphere from this observation. In this work, we have taken into account the influence of the recombination delay effect during gas motion in the stellar magnetosphere. The accounting for this effect and the presence of the magnetospheric absorption in the IR Ca ii triplet lines and its absence in D Na i resonance lines allowed us to place a lower limit on the temperature in the magnetosphere at $\approx 10\, 000$ K, which significantly improved precision of our estimate of accretion rate. According to the best-fitting model, the logarithm of accretion rate is $\log \dot{M} = -10.1\pm 0.3$ ($\dot{M} \approx 7\times 10^{-11}\ \mathrm{M_\odot \, yr^{-1}}$) and the inclination angle of RZ Psc is 43° ± 3°. It is less than the inclination, typical for the UX Ori stars (about 70°), that explains the weak photometric variability of this star. Using the obtained accretion rate and magnetosphere radius, we estimate the strength of the dipole component of the magnetic field of RZ Psc ≈ 0.1 kGs.

A CCD search for variable stars in the open cluster NGC 6611

ABSTRACT We present the results of the UBVIC variability survey in the young open cluster NGC 6611 based on observations obtained during 34 nights spanning one year. In total, we found 95 variable stars. Most of these stars are classified as periodic and irregular pre-main sequence (PMS) stars. The analysis of the JHKS 2MASS photometry and four-colour IRAC photometry revealed 165 Class II young stellar sources, 20 of which are irregular variables and one is an eclipsing binary. These classifications, complemented by JHK UKIDSS photometry and riHα VPHAS photometry, were used to identify 24 candidates for classical T Tauri stars and 30 weak-lined T Tauri stars. In addition to the PMS variables, we discovered eight δ Scuti candidates. None of these were previously known. Furthermore, we detected 17 eclipsing binaries where two were previously known. Based on the proper motions provided by the Gaia EDR3 catalogue, we calculated the cluster membership probabilities for 91 variable stars. For 61 variables, a probability higher than 80 per cent was determined, which makes them cluster members. Only 25 variables with a probability less than 20 per cent were regarded to be non-members.

NEOWISE Variability of the New Gaia Herbig Ae/Be and Classical Be Stars—Variability Sample and Statistical Analysis

Light variability is an essential attribute of young stellar objects (YSOs) at the pre-main-sequence (PMS) stage, which can be treated as an indicator to trace star formation. We present a statistical study on the infrared NEOWISE variability of new and large-sized PMS stars as well as Herbig Ae/Be (HAeBe) and classical Be (CBe) stars identified from Gaia Data Release 2. A total of 3792 (including 714 HAeBe), 417, and 473 NEOWISE variable sources were detected from the catalog of 8470 PMS (including 1361 HAeBe), 693 CBe, and 1309 uncertain (possibly belonging to either HAeBe or CBe) stars, respectively. We found that 80% of the PMS variables are dominated by irregular infrared variability, whereas variables in the CBe and uncertain categories exhibit comparable contributions from secular (linear, curved, and periodic) and stochastic (burst, drop, and irregular) variables. This, in combination with infrared W1–W2 colors, W4 luminosities, and the spectral energy distribution slope at near- and mid-infrared wavelengths, suggests different evolutionary stages of the PMS (including HAeBe), uncertain, and CBe stars, from less to more evolved. A statistical analysis of variable source properties (e.g., period and fractional amplitude) further reveals a potential sequence possibly associated with disk evolution for different types of light curves (from linear, to curved, periodic, stochastic, and nonvariable stars). Possible mechanisms for the variable sources are suggested to be related to either extinction via circumstellar matter, or contribution of multiple systems surrounding the YSOs, as opposed to variable accretion (e.g., episodic accretion or accretion burst).

The GRAVITY young stellar object survey

Context. Hot atomic hydrogen emission lines in pre-main sequence stars serve as tracers for physical processes in the innermost regions of circumstellar accretion disks, where the interaction between a star and disk is the dominant influence on the formation of infalls and outflows. In the highly magnetically active T Tauri stars, this interaction region is particularly shaped by the stellar magnetic field and the associated magnetosphere, covering the inner five stellar radii around the central star. Even for the closest T Tauri stars, a region as compact as this is only observed on the sky plane at sub-mas scales. To resolve it spatially, the capabilities of optical long baseline interferometry are required. Aims. We aim to spatially and spectrally resolve the Brγ hydrogen emission line with the methods of interferometry in order to examine the kinematics of the hydrogen gas emission region in the inner accretion disk of a sample of solar-like young stellar objects. The goal is to identify trends and categories among the sources of our sample and to discuss whether or not they can be tied to different origin mechanisms associated with Brγ emission in T Tauri stars, chiefly and most prominently magnetospheric accretion. Methods. We observed a sample of seven T Tauri stars for the first time with VLTI GRAVITY, recording spectra and spectrally dispersed interferometric quantities across the Brγ line at 2.16 µm in the near-infrared K-band. We used the visibilities and differential phases to extract the size of the Brγ emission region and the photocentre shifts on a channel-by-channel basis, probing the variation of spatial extent at different radial velocities. To assist in the interpretation, we also made use of radiative transfer models of magnetospheric accretion to establish a baseline of expected interferometric signatures if accretion is the primary driver of Brγ emission. Results. From among our sample, we find that five of the seven T Tauri stars show an emission region with a half-flux radius in the four to seven stellar radii range that is broadly expected for magnetospheric truncation. Two of the five objects also show Brγ emission primarily originating from within the co-rotation radius, which is an important criterion for magnetospheric accretion. Two objects exhibit extended emission on a scale beyond 10 R*, one of them is even beyond the K-band continuum half-flux radius of 11.3 R*. The observed photocentre shifts across the line can be either similar to what is expected for disks in rotation or show patterns of higher complexity. Conclusions. Based on the observational findings and the comparison with the radiative transfer models, we find strong evidence to suggest that for the two weakest accretors in the sample, magnetospheric accretion is the primary driver of Brγ radiation. The results for the remaining sources imply either partial or strong contributions coming from additional, spatially extended emission components in the form of outflows, such as stellar or disk winds. We expect that in actively accreting T Tauri stars, these phenomena typically occur simultaneously on different spatial scales. Through more advanced modelling, interferometry will be a key factor in disentangling their distinct contributions to the total Brγ flux arising from the innermost disk regions.

Long-term Photometric Study of the Pre-main Sequence Star V1180 Cas

In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported. The star is a young variable associated with the dark cloud Lynds 1340, located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia. V1180 Cas shows large amplitude variability, interpreted as a combination of accretion-induced and extinction-driven effects. Our data from VRI CCD photometric observations of the star were collected from September 2011 to February 2022. During our monitoring, we recorded several brightness dips with large amplitudes of up to 5 mag (I band). At the same time, increases in brightness over periods of several weeks have also been recorded. In this paper, we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.

A Low-mass Pre-main-sequence Eclipsing Binary in Lower Centaurus Crux Discovered with TESS

We report the discovery of 2M1222−57 as a low-mass, pre-main-sequence (PMS) eclipsing binary (EB) in the Lower Centaurus Crux (LCC) association for which, using Gaia parallaxes and proper motions with a neural net age estimator, we determine an age of 16.2 ± 2.2 Myr. The broadband spectral energy distribution (SED) shows clear excess at ≳10 μm indicative of a circumbinary disk, and new speckle imaging observations reveal a faint, tertiary companion separated by ∼100 au. Hα emission is modulated on the orbital period, consistent with theoretical models of orbitally pulsed accretion streams reaching from the inner disk edge to the central stars. From a joint analysis of spectroscopically determined radial velocities and TESS light curves, together with additional tight constraints provided by the SED and the Gaia parallax, we measure masses for the eclipsing stars of 0.74 M ⊙ and 0.67 M ⊙; radii of 0.98 R ⊙ and 0.94 R ⊙; and effective temperatures of 3750 K and 3645 K. The masses and radii of both stars are measured to an accuracy of ∼1%. The measured radii are inflated, and the temperatures suppressed, relative to predictions of standard PMS evolutionary models at the age of LCC; also, the Li abundances are ∼2 dex less depleted than predicted by those models. However, models that account for the global and internal effects of surface magnetic fields are able to simultaneously reproduce the measured radii, temperatures, and Li abundances at an age of 17.0 ± 0.5 Myr. Altogether, the 2M1222−57 system presents very strong evidence that magnetic activity in young stars alters both their global properties and the physics of their interiors.

H2O masers and host environments of FU Orionis and EX Lupi type low-mass eruptive YSOs

AbstractThe FU Orionis (FUor) and EX Lupi (EXor) type objects are rare pre-main sequence low-mass stars undergoing accretion outbursts. Maser emission is widespread and is a powerful probe of mass accretion and ejection on small scales in star forming region. However, very little is known about the overall prevalence of water masers towards FUors/Exors. We present results from our survey using the Effelsberg 100-m telescope to observe the largest sample of FUors and EXors, plus additional Gaia alerted sources (with the potential nature of being eruptive stars), a total of 51 targets, observing the 22.2 GHz H2O maser, while simultaneously covering the NH3 23 GHz.

Analyses of hydrogen-stripped core–collapse supernovae using MOSFiT and MESA-based tools

In this work, we employ two publicly available analysis tools to study four hydrogen(H)--stripped core--collapse supernovae (CCSNe) namely, SN 2009jf, iPTF13bvn, SN 2015ap, and SN 2016bau. We use the Modular Open-Source Fitter for Transients ({\tt MOSFiT}) to model the multi band light curves. {\tt MOSFiT} analyses show ejecta masses (log M$_{ej}$) of $0.80_{-0.13}^{+0.18}$ M$_{\odot}$, $0.15_{-0.09}^{+0.13}$ M$_{\odot}$, $0.19_{-0.03}^{+0.03}$ M$_{\odot}$, and $0.19_{+0.02}^{-0.01}$ M$_{\odot}$ for SN 2009jf, iPTF13vn, SN 2015ap, and SN 2016au, respectively. Later, Modules for Experiments in Stellar Astrophysics ({\tt MESA}), is used to construct models of stars from pre-main sequence upto core collapse which serve as the possible progenitors of these H-stripped CCSNe. Based on literature, we model a 12 M$_{\odot}$ ZAMS star as the possible progenitor for iPTF13vn, SN 2015ap, and SN 2016bau while a 20 M$_{\odot}$ ZAMS star is modeled as the possible progenitor for SN 2009jf. Glimpses of stellar engineering and the physical properties of models at various stages of their lifetime have been presented to demonstrate the usefulness of these analysis threads to understand the observed properties of several classes of transients in detail.

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

ABSTRACT Classical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass (∼ 0.6 M⊙) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman–Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse.