Characterization of the dynamics of massive star systems and the astrophysical properties of the interacting components are a prerequisite for understanding their formation and evolution. Optical ...interferometry at milliarcsecond resolution is a key observing technique for resolving high-mass multiple compact systems. Here, we report on Very Large Telescope Interferometer/GRAVITY, Magellan/Folded-port InfraRed Echellette, and MPG2.2 m/FEROS observations of the late-O/early-B type system HD 93206 A, which is a member of the massive cluster Collinder 228 in the Carina nebula complex. With a total mass of about , it is one of the most compact massive quadruple systems known. In addition to measuring the separation and position angle of the outer binary Aa-Ac, we observe Brγ and He i variability in phase with the orbital motion of the two inner binaries. From the differential phase ( ) analysis, we conclude that the Brγ emission arises from the interaction regions within the components of the individual binaries, which is consistent with previous models for the X-ray emission of the system based on wind-wind interaction. With an average 3 deviation of , we establish an upper limit of p ∼ 0.157 mas (0.35 au) for the size of the Brγ line-emitting region. Future interferometric observations with GRAVITY using the 8 m Unit Telescopes will allow us to constrain the line-emitting regions down to angular sizes of 20 as (0.05 au at the distance of the Carina nebula).
We perform a detailed computational study of the recently introduced Sombor indices on random networks. Specifically, we apply Sombor indices on three models of random networks: Erdös-Rényi networks, ...random geometric graphs, and bipartite random networks. Within a statistical random matrix theory approach, we show that the average values of Sombor indices, normalized to the order of the network, scale with the average degree. Moreover, we discuss the application of average Sombor indices as complexity measures of random networks and, as a consequence, we show that selected normalized Sombor indices are highly correlated with the Shannon entropy of the eigenvectors of the adjacency matrix.
We observe the high-mass X-ray binary (HMXB) BP Cru using interferometry in the near-infrared K band with VLTI/GRAVITY. Continuum visibilities are at most partially resolved, consistent with the ...predicted size of the hypergiant. Differential visibility amplitude ( ) and phase ( ) signatures are observed across the He i and Brγ lines, the latter seen strongly in emission, unusual for the donor star's spectral type. For a baseline m, the differential phase rms corresponds to an astrometric precision of . We generalize expressions for image centroid displacements and variances in the marginally resolved limit of interferometry to spectrally resolved data, and use them to derive model-independent properties of the emission such as its asymmetry, extension, and strong wavelength dependence. We propose geometric models based on an extended and distorted wind and/or a high-density gas stream, which has long been predicted to be present in this system. The observations show that optical interferometry is now able to resolve HMXBs at the spatial scale where accretion takes place, and therefore to probe the effects of the gravitational and radiation fields of the compact object on its environment.
Abstract
The time that waves spend inside 1D random media with the possibility of performing Lévy walks is experimentally and theoretically studied. The dynamics of quantum and classical wave ...diffusion has been investigated in canonical disordered systems via the delay time. We show that a wide class of disorder—Lévy disorder—leads to strong random fluctuations of the delay time; nevertheless, some statistical properties such as the tail of the distribution and the average of the delay time are insensitive to Lévy walks. Our results reveal a universal character of wave propagation that goes beyond standard Brownian wave-diffusion.
We present high spatial resolution mid-infrared images of the nebula around the late-type carbon-rich Wolf-Rayet (WC)-OB binary system WR 112 taken by the recently upgraded VLT spectrometer and ...imager for the mid-infrared (VISIR) with the PAH1, Ne ii_2, and Q3 filters. The observations reveal a morphology resembling a series of arc-like filaments and broken shells. Dust temperatures and masses are derived for each of the identified filamentary structures, which exhibit temperatures ranging from K at the exterior W2 filament to K in the central 3″. The total dust mass summed over the features is 2.6 0.4 × 10−5 M . A multi-epoch analysis of mid-IR photometry of WR 112 over the past ∼20 years reveals no significant variability in the observed dust temperature and mass. The morphology of the mid-IR dust emission from WR 112 also exhibits no significant expansion from imaging data taken in 2001, 2007, and 2016, which disputes the current interpretation of the nebula as a high expansion velocity (∼1200 km s−1) "pinwheel"-shaped outflow driven by the central WC-OB colliding-wind binary. An upper limit of 120 km s−1 is derived for the expansion velocity assuming a distance of 4.15 kpc. The upper limit on the average total mass-loss rate from the central 3″ of WR 112 is estimated to be 8 × 10−6 M year−1. We leave its true nature as an open question, but propose that the WR 112 nebula may have formed in the outflow during a previous red or yellow supergiant phase of the central Wolf-Rayet star.
Context. HD 50138 is a Herbig Be star with a circumstellar disc detected at infrared and millimeter wavelength. Its brightness makes it a good candidate for near-infrared interferometry observations. ...Aims. We aim to resolve, spatially and spectrally, the continuum and hydrogen emission lines in the 2.12–2.47 micron region, to shed light on the immediate circumstellar environment of the star. Methods. VLTI/AMBER K-band observations provide spectra, visibilities, differential phases, and closure phases along three long baselines for the continuum, and H I emission in Brγ and five high-n Pfund lines. By computing the pure line visibilities, we derive the angular size of the different line-emitting regions. A simple local thermodynamic equilibrium (LTE) model was created to constrain the physical conditions of H I emitting region. Results. The continuum region cannot be reproduced by a geometrical two-dimensional (2D) elongated Gaussian fitting model. We estimate the size of the region to be 1 au. We find the detected hydrogen lines (Brγ and Pfund lines) come from a more compact region of size 0.4 au. The Brγ line exhibits an S-shaped differential phase, indicative of rotation. The continuum and Brγ line closure phases show offsets of ~ −25 ± 5° and 20 ± 10° respectively. This is evidence of an asymmetry in their origin, but with opposing directions. We find that we cannot converge on constraints for the HI physical parameters without a more detailed model. Conclusions. Our analysis reveals that HD 50138 hosts a complex circumstellar environment. Its continuum emission cannot be reproduced by a simple disc brightness distribution. Similarly, several components must be evoked to reproduce the interferometric observables within the Brγ line. Combining the spectroscopic and interferometric data of the Brγ and Pfund lines favours an origin in a wind region with a large opening angle. Finally, although we cannot exclude the possibility that HD 50138 is a young star our results point to an evolved source.
The little-studied cluster Berkeley 90 Apellaniz, J Maiz; Negueruela, I; Barba, R H ...
Astronomy and astrophysics (Berlin),
7/2015, Letnik:
579
Journal Article
Recenzirano
Odprti dostop
Context. It appears that most (if not all) massive stars are born in multiple systems. At the same time, the most massive binaries are hard to find owing to their low numbers throughout the Galaxy ...and the implied large distances and extinctions. Aims. We want to study LS III +46 11, identified in this paper as a very massive binary; another nearby massive system, LS III +46 12; and the surrounding stellar cluster, Berkeley 90. Methods. Most of the data used in this paper are multi-epoch high S/N optical spectra, although we also use Lucky Imaging and archival photometry. The spectra are reduced with dedicated pipelines and processed with our own software, such as a spectroscopic-orbit code, CHORIZOS, and MGB. Results. LS III +46 11 is identified as a new very early O-type spectroscopic binary O3.5 If* + O3.5 If* and LS III +46 12 as another early O-type system O4.5 V((f)). We measure a 97.2-day period for LS III +46 11 and derive minimum masses of 38.80 + or - 0.83 M sub(middot in circle) and 35.60 + or - 0.77 M sub(middot in circle) for its two stars. We measure the extinction to both stars, estimate the distance, search for optical companions, and study the surrounding cluster. In doing so, a variable extinction is found as well as discrepant results for the distance. We discuss possible explanations and suggest that LS III +46 12 may be a hidden binary system where the companion is currently undetected.
Endocannabinoid signaling has recently been implicated in ethanol-seeking behavior. We analyzed the expression of endocannabinoid-related genes in key brain regions of reward and dependence, and ...compared them between the alcohol-preferring AA (Alko Alcohol) and nonpreferring ANA (Alko Non-Alcohol) rat lines. A decreased expression of fatty acid amidohydrolase (FAAH), the main endocannabinoid-degrading enzyme, was found in prefrontal cortex (PFC) of AA rats, and was accompanied by decreased enzyme activity in this region. Binding of the endocannabinoid-cannabinoid 1 (CB1) receptor ligand (3)HSR141716A, and 35SGTPgammaS incorporation stimulated by the CB1 agonist WIN 55,212-2 were downregulated in the same area. Together, this suggests an overactive endocannabinoid transmission in the PFC of AA animals, and a compensatory downregulation of CB1 signaling. The functional role of impaired FAAH function for alcohol self-administration was validated in two independent ways. The CB1 antagonist SR141716A potently and dose-dependently suppressed self-administration in AA rats when given systemically, or locally into the PFC, but not in the striatum. Conversely, intra-PFC injections of the competitive FAAH inhibitor URB597 increased ethanol self-administration in nonselected Wistar rats. These results show for the first time that impaired FAAH function may confer a phenotype of high voluntary alcohol intake, and point to a FAAH both as a potential susceptibility factor and a therapeutic target.
Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis ~15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, η Car ...A, is a luminous blue variable (LBV); the secondary, η Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV η Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of η Car’s WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Brα imaging of η Car’s distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of η Car A’s stellar windin several spectral channels distributed across the Brα 4.052 μm line (spectral resolving power R ~ 960). Our observations were performed close to periastron passage in February 2020 (orbital phase ~ 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (~14 au). The radius of the faintest outer wind regions is ~26 mas (~60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 ± 0.06 mas (6.54 ± 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
In this work we perform analytical and statistical studies of the Rodríguez–Velázquez (
RV
) indices on graphs
G
. The topological
RV
(
G
) indices, recently introduced in Rodríguez–Velázquez and ...Balaban (J Math Chem 57:1053, 2019), are based on graph adjacency matrix eigenvalues and eigenvectors. First, we analytically obtain new relations connecting
RV
(
G
) with the graph energy
E
(
G
) and the subgraph centrality
EE
(
G
), the later being proportional to the well known Estrada index. Then, within a random matrix theory (RMT) approach we statistically validate our relations on ensembles of randomly-weighted Erdős–Rényi graphs
G
(
n
,
p
), characterized by
n
vertices connected independently with probability
p
∈
(
0
,
1
)
. Additionally, we show that the ratio
R
V
(
G
(
n
,
p
)
)
/
R
V
(
G
(
n
,
0
)
)
scales with the average degree
k
=
(
n
-
1
)
p
.
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