A High Spatial Resolution Infrared View of the T Tauri Multiple System

We present results from our spectroscopic follow-up of SDSS J2320+0024, a candidate binary supermassive black hole (SMBH) with a suspected subparsec separation, identified by a 278-day periodicity observed in its multiband optical light curves. Such systems serve as a crucial link between binaries with long periods (tens of years), which are influenced by tidal forces with minimal gravitational wave damping, and ultra-short-period binaries (≤ order of days), which are dominated by gravitational wave-driven inspiral. We investigated the dramatic variability in the complex emission line profile with the aim of testing the alignments of the observed photometric light curves and the spectroscopic signatures in the context of the binary SMBH system. We extracted the pure broad line from newly obtained Gemini and Magellan spectra and measured the emission line parameters to determine the fundamental dynamical parameters of the SMBH's binary system. We adopted the PoSKI subparsec binary SMBH model, which includes a broad-line region around a less massive component and a circumbinary broad-line region, to interpret the observed variability in the spectral profile. We find that the broad-line profile has a distinctive complex shape, with asymmetry and two peaks, which has varied across recent and archival observations. The temporal variability of the line profile may be associated with emission from the binary SMBH system, whose components have masses ( M_1 = 2 ⊙ ) and ( M_2 = 2 ⊙ ) and eccentricity e = 0.1. We discuss other plausible physical interpretations. With a total estimated mass of ∼ 10^9 ⊙ and a sub-annual orbital period, this system may be a rare example of a high-mass compact SMBH binary candidate and, thus, should be part of further investigations of the evolution of binary systems. This study highlights the synergies between spectroscopic follow-up and future massive time-domain photometric surveys, such as the Vera C. Rubin Observatory Legacy Survey of Space and Time.

As far as we now know, interstellar dust and the diffuse interstellar bands (DIBs) are not directly related; there is no really good correlation between any DIB and a specific feature of interstellar extinction. I argue that it is not useful to consider the λ2175 “bump”, by far the strongest feature in the interstellar extinction law (in terms of equivalent width in frequency units), a bona fide DIB. The bump is probably not formed by the same processes that cause the DIBs; it is so strong that it is almost surely produced by carbon in some form (probably graphitic), likely by a different physical process (a plasma resonance rather than a bulk resonance). However, the bump’s broadening, which might well be produced by coatings on graphitic grains. suggests that there are rather efficient interactions between grains and the material that produces the coatings. The systematics of the interstellar extinction law among various lines of sight also strongly suggests rapid interactions among grains of various sizes, since apparently the small grains coagulate into large ones in dense-gas environments.Interstellar depletions, or removel of certain gas-phase of the ISM onto grains, also provide strong evidence for interactions of grains and gas atoms. Nonthermal motions of the grains are very likely required to produce the depletion observations. These rapid interactions must also apply to the carries of the DIBs, so they must be capable of temporarily residing on grains surfaces or else being formed very rapidly in the gas phase. The quantitative determination of depletions is confused by the selection of reference abundances, or total elemental abundances (relative to H) in the ISM. There seem to be incompatible observations regarding wherther the solar abundances or those of B stars should be preferred. In any case, along one line of C used to produce DIBs and visual extinction is limited. It is not at all understood why certain elements are strongly depleted and others are only lightly so.KeywordsEquivalent WidthPlasma ResonanceInterstellar DustInterstellar ExtinctionSolar AbundanceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The irregular photometric variability of the triple system T Tauri has been puzzling since its discovery. A circumbinary disk around T Tau Sa and Sb can explain the recent brightness fluctuations of T Tau Sb, due to changes in extinction depending on the position of T Tau Sb in its orbit. The photometric variations and orbital motion of T Tau Sb indicate a position angle of the disk of ∼30°. Combined with information from the literature, we estimate its inclination to be ∼60° or more.

We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond, (2) average over dust compositions, and (3) mischaracterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly overestimated. In particular, the stellar luminosity is most likely in the range 104.8 < L */L ☉ < 105.0 and the star was not extremely massive for a Type IIP progenitor, with M * < 15 M ☉. Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw, the star was probably obscured by an ongoing wind with to 10−5.0 M ☉ yr−1 at the time of the explosion, roughly consistent with the expected mass-loss rates for a star of its temperature (T * ≃ 3600+300 − 200 K) and luminosity. In the spirit of Galactic extinction laws, we supply simple interpolation formulae for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength (λ ⩾ 0.3 μm) and total (absorption plus scattering) V-band optical depth (τ V ⩽ 20). These do not include the contributions of dust emission, but provide a simple, physical alternative to incorrectly using interstellar extinction laws.

The interstellar extinction law is important for interpreting observations and inferring the properties of interstellar dust grains. Based on the 993 prism/CLEAR spectra from the James Webb Space Telescope (JWST), we investigate the 0.6–5.3 μm interstellar dust extinction law. We propose a pair method to obtain the reddening curves based only on JWST observed spectra. Most of the high-extinction sources are toward the young star cluster Westerlund 2. The infrared 1.0–5.3 μm reddening curves agree with the power law A λ ∝ λ −α well. We determine an average value of α = 1.98 ± 0.15, which is consistent with the average value of the Galaxy. We find that α may be variable and independent of R V . With the derived α, we convert the reddening curves into the extinction curves and establish the nonparameterized α-dependent extinction curves in the wavelength range of 0.6–5.3 μm. At λ < 1 μm, the derived extinction law is not well described by the parameterized power-law-type curve. Our nonparameterized α-dependent extinction curves are suitable for the extinction correction of JWST-based photometry and spectra measurements at 0.6–5.3 μm. We also provide the extinction coefficients for the JWST NIRCam bandpasses with different α.

With high-angular-resolution, near-infrared observations of the young stellar object T Tauri at the end of 2002, we show that, contrary to previous reports, none of the three infrared components of T Tau coincide with the compact radio source that has apparently been ejected recently from the system (Loinard, Rodriguez, and Rodriguez 2003). The compact radio source and one of the three infrared objects, T Tau Sb, have distinct paths that depart from orbital or uniform motion between 1997 and 2000, perhaps indicating that their interaction led to the ejection of the radio source. The path that T Tau Sb took between 1997 and 2003 may indicate that this star is still bound to the presumably more massive southern component, T Tau Sa. The radio source is absent from our near-infrared images and must therefore be fainter than K = 10.2 (if located within 100 mas of T Tau Sb, as the radio data would imply), still consistent with an identity as a low-mass star or substellar object.

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We investigate the prospects for constraining the maximum scale of clumping in composition that is consistent with observed Type Ia supernova flux spectra. Synthetic spectra generated without purely spherical composition symmetry indicate that gross asymmetries make prominent changes to absorption features. Motivated by this, we consider the case of a single unblended line forming in an atmosphere with perturbations of different scales and spatial distributions. Perturbations of about 1% of the area of the photodisk simply weaken the absorption feature by the same amount independent of the line of sight. Conversely, perturbations of about 10% of the area of the photodisk introduce variation in the absorption depth which does depend on the line of sight. Thus, 1% photodisk area perturbations may be consistent with observed profile homogeneity but 10% photodisk area perturbations can not. Based on this, we suggest that the absence of significant variation in the depths of Si II 6355 absorption features in normal Type Ia spectra near maximum light indicates that any composition perturbations in these events are quite small. This also constrains future three-dimensional explosion models to produce ejecta profiles with only small scale inhomogeneities.

We present new photometric data and LAMOST spectra for the W UMa binaries UV Lyn, V781 Tau, NSVS 4484038, and 2MASS J15471055+5302107. The orbital and starspot parameters are obtained using the Wilson–Devinney program. Comparing the starspot parameters at different times, there are magnetic activities in these four binaries. The orbital period of UV Lyn is increasing at a rate of dP/dt = +8.9(5) × 10−8 days yr−1, which maybe due to mass transfer from the less massive component to the more massive component (dM 1/dt = −6.4 × 10−8 M ⊙ yr−1). The period variation of 2MASS J15471055+5302107 is also increasing at a rate of 6.0(4) × 10−7 days yr−1, which can be explained by mass transfer from the less massive component to the more massive component (dM 1/dt = −2.8 × 10−7 M ⊙ yr−1). The period variation of V781 Tau presents the downward parabola superimposed the cyclic oscillation. The period of V781 Tau is decreasing (dP/dt = −3.2(4) × 10−8 days yr−1), which can be explained by mass transfer from the more massive component to the less massive component (dM 2/dt = −2.2 × 10−8 M ⊙ yr−1). The cyclic oscillation may be due to the magnetic activity with a period of 30.8(5) yr rather than a third body. The period variation of NSVS 4484038 also shows the cyclic oscillation, which could be explained by the magnetic activity with 10.8(1) yr or a black hole candidate. Interestingly, there is a depth variation between the light minimum times of NSVS 4484038, which may also be caused by stellar magnetic activity.

The southern dark globule DC 314.8-5.1 contains a reflection nebula illuminated by a normal B9 V star, HD 130079. This serendipitous association provides the opportunity to evaluate the distance to the globule with greater accuracy than would otherwise be possible, subject to accurate accounting for the effects of interstellar extinction and reddening. It is shown that the dust in the line of sight has optical properties characterized by elevated values of the ratio of extinction to reddening (RV = AV/EB-V) and the wavelength of maximum polarization (λmax), signifying growth that most probably results from grain-grain coagulation within the globule. Taking this into account yields a distance of 342 ± 50 pc, significantly lower than previous estimates that assume the standard diffuse interstellar medium average extinction law. Comparison of this result with the loci of other major sources of extinction along the line of sight suggests that the globule is isolated; it appears to not be physically associated with the adjacent Circinus molecular cloud and star formation complex G317.0-4.0. Estimates are made of the mean number density (nH ≳ 9 × 103 cm-3) and mass (30-100 M⊙) of DC 314.8-5.1. A stellar census of the region using the Two Micron All Sky Survey suggests that it is not a site of vigorous star formation, although two (out of 387) sources are identified that appear to be good candidates for young stellar object status on the basis of their near-infrared colors. A deep mid-infrared survey will be needed to determine whether DC 314.8-5.1 is, indeed, starless (with respect to indigenous birth) or a site of sedentary low-mass star formation. The globule may also prove to be a valuable laboratory for future study of the interaction of dense molecular gas and dust in a quiescent core with the relatively soft UV radiation field emanating from the embedded B9 V star.

We determine the interstellar extinction in the selected high-latitude areas of the sky based on Gaia EDR3 astrometry and photometry and spectroscopic data from RAVE survey. We approximate the results with the cosecant law in each area thus deriving the parameters of the barometric formula for different lines of sight. The distribution of the parameters over the entire sky is described using spherical harmonics. As a result, we get a mathematical description of the interstellar visual extinction for different lines of sight and distances from the Sun which can be used for estimating interstellar extinction.

In many models of dusty objects in space the grains are assumed to be composite or fluffy. However, the computation of the optical properties of such particles is still a very difficult problem. We analyze how the increase of grain porosity influences basic features of cosmic dust – interstellar extinction, dust temperature, infrared bands and millimeter opacity. It is found that an increase of porosity leads to an increase of extinction cross sections at some wavelengths and a decrease at others depending on the grain model. However, this behaviour is sufficient to reproduce the extinction curve in the direction of the star σ Sco using current solar abundances. In the case of the star ζ Oph our model requires larger amounts of carbon and iron in the dust-phase than is available. Porous grains can reproduce the flat extinction across the $3 {-} 8\,\mu{\rm m}$ wavelength range measured for several lines of sight by ISO and Spitzer. Porous grains are generally cooler than compact grains. At the same time, the temperature of very porous grains becomes slightly larger in the case of the EMT-Mie calculations in comparison with the results found from the layered-sphere model. The layered-sphere model predicts a broadening of infrared bands and a shift of the peak position to larger wavelengths as porosity grows. In the case of the EMT-Mie model variations of the feature profile are less significant. It is also shown that the millimeter mass absorption coefficients grow as porosity increases with a faster growth occurring for particles with Rayleigh/non-Rayleigh inclusions. As a result, for very porous particles the coefficients given by two models can differ by a factor of about 3.

Effects of irrigation level and timing on profile soil water use by grain sorghum

The most striking characteristics of the mysterious 2175$\mathring{\rm A}$ extinction bump, the strongest spectroscopic absorption feature seen on the interstellar extinction curve, are the invariant central wavelength and variable bandwidth: its peak position at 2175$\mathring{\rm A}$ is remarkably constant, while its bandwidth varies from one line of sight to another. However, recent studies of the lines of sight towards a number of Herbig Ae/Be stars have revealed that the extinction bump exhibits substantial shifts from the canonical wavelength of 2175$\mathring{\rm A}$. In this work, we revisit these lines of sight and take a physical approach to determine the ultraviolet (UV) extinction curve for each line of sight. It is found that the wavelengths of the derived UV extinction bumps are around 2200$\mathring{\rm A}$ and the scatters are considerably smaller than those of the previous study based on the same set of Herbig Ae/Be stars, consistent with the conventional wisdom of a stable bump position. Nevertheless, the scatters are still appreciably larger than those associated with the nominal bump position of 2175$\mathring{\rm A}$. This is discussed in the context that Herbig Ae/Be stars are not well suited for interstellar extinction studies.

Context.The evolution of massive stars is dominated by interactions within binary and multiple systems. In order to accurately model this evolution, it is necessary to investigate all possible forms of an interaction in binary systems that may affect the evolution of the components. One of the “laboratories” plausible for this kind of investigation is the massive eccentric binary system MACHO 80.7443.1718 (ExtEV), which exhibits an exceptionally large amplitude of light variability close to the periastron passage of its 32.8-day orbit.Aims.We examine whether the light variability of ExtEV can be explained by a wind-wind collision (WWC) binary system model. We also critically review other models proposed to explain the light curve of ExtEV.Methods.We conducted an analysis of (i) the broadband multicolor photometry of ExtEV spanning a wide range of wavelengths from the ultraviolet to near-infrared, (ii) the time-series space photometry from the Transiting Exoplanet Survey Satellite (TESS), (iii) ground-based JohnsonUBVphotometry, and (iv) time-series high-resolution spectroscopy. To derive the parameters of the primary component of the system, we fit the spectral energy distribution (SED) and calculated evolutionary models of massive stars that included mass loss. Using radial-velocity data, we determined the spectroscopic parameters of the system. We also fit an analytical model of light variations to the TESS light curve of ExtEV.Results.The ExtEV system exhibits an infrared excess, indicating an increased mass-loss rate. The system does not match the characteristics of B[e] stars, however. We rule out the possibility of the presence of a Keplerian disk around the primary component. We also argue that the scenario with periodic Roche-lobe overflow at periastron may not be consistent with the observations of ExtEV. Analysis of the SED suggests that the primary component has a radius of about 30R⊙and a luminosity of ∼6.6 × 105L⊙. With the analysis of the radial-velocity data, we refine the orbital parameters of ExtEV and find evidence for the presence of a tertiary component in the system. Using evolutionary models we demonstrate that the primary component’s mass is between 25 and 45M⊙. We successfully reproduced the light curve of ExtEV with our analytical model, showing that the dominant processes shaping its light curve can be attributed to the atmospheric eclipse and light scattered in the WWC cone. We also estimate the primary’s mass loss rate due to stellar wind for 4.5 × 10−5M⊙yr−1.Conclusions.ExtEV is most likely not an extreme eccentric ellipsoidal variable, but rather an exceptional WWC binary system. The mass loss rate we derived exceeds theoretical predictions by up to two orders of magnitude. This implies that the wind in the system is likely enhanced by tidal interactions, rotation, and possibly also tidally excited oscillations. Therefore, ExtEV represents a rare evolutionary phase of a binary system that may help to understand the role of companion-driven enhanced mass loss in the evolution of massive binary systems.