An official website of the United States government
Abstract Emission lines from Rydberg transitions are detected for the first time from a region close to the surface of Betelgeuse. The H30αline is observed at 231.905 GHz, with an FWHM ∼42 km s−1and extended wings. A second line at 232.025 GHz (FWHM ∼21 km s−1), is modeled as a combination of Rydberg transitions of abundant low first ionization potential metals. Both H30αand the Rydberg combined line X30αare fitted by Voigt profiles, and collisional broadening with electrons may be partly responsible for the Lorentzian contribution, indicating electron densities of a few 108cm−3. X30αis located in a relatively smooth ring at a projected radius of 0.9× the optical photospheric radiusR⋆, whereas H30αis more clumpy, reaching a peak at ∼1.4R⋆. We use a semiempirical thermodynamic atmospheric model of Betelgeuse to compute the 232 GHz (1.29 mm) continuum and line profiles making simple assumptions. Photoionized abundant metals dominate the electron density, and the predicted surface of continuum optical depth unity at 232 GHz occurs at ∼1.3R⋆, in good agreement with observations. Assuming a Saha–Boltzmann distribution for the level populations of Mg, Si, and Fe, the model predicts that the X30αemission arises in a region of radially increasing temperature and turbulence. Inclusion of ionized C and non-LTE effects could modify the integrated fluxes and location of emission. These simulations confirm the identity of the Rydberg transition lines observed toward Betelgeuse and reveal that such diagnostics can improve future atmospheric models.
more »
« less
The 107 GHz Methanol Transition Is a Dasar in G0.253+0.016
Abstract We present observations of population anti-inversion in the 31− 40A+transition of CH3OH (methanol) at 107.013831 GHz toward the Galactic center cloud G0.253+0.016 (“The Brick”). Anti-inversion of molecular level populations can result in absorption lines against the cosmic microwave background (CMB) in a phenomenon known as a “dasar.” We model the physical conditions under which the 107 GHz methanol transition dases and determine that dasing occurs at densities below 106cm−3and column densities between 1013and 1016cm−2. We also find that for this transition, dasing does not strongly depend on the gas kinetic temperature. We evaluate the potential of this tool for future deep galaxy surveys. We note that other works have already reported absorption in this transition (e.g., in NGC 253), but we provide the first definitive evidence that it is absorption against the CMB rather than against undetected continuum sources.
more »
« less
- PAR ID:
- 10468396
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 956
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 78
- Size(s):
- Article No. 78
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT Triplet arylnitrenes may provide direct access to aryl azo‐dimers, which have broad commercial applicability. Herein, the photolysis ofp‐azidostilbene (1) in argon‐saturated methanol yielded stilbene azo‐dimer (2) through the dimerization of tripletp‐nitrenostilbene (31N). The formation of31Nwas verified by electron paramagnetic resonance spectroscopy and absorption spectroscopy (λmax ~ 375 nm) in cryogenic 2‐methyltetrahydrofuran matrices. At ambient temperature, laser flash photolysis of1in methanol formed31N(λmax ~ 370 nm, 2.85 × 107 s−1). On shorter timescales, a transient absorption (λmax ~ 390 nm) that decayed with a similar rate constant (3.11 × 107 s−1) was assigned to a triplet excited state (T) of1. Density functional theory calculations yielded three configurations for T of1, with the unpaired electrons on the azido (TA) or stilbene moiety (TTw, twisted and TFl, flat). The transient was assigned to TTwbased on its calculated spectrum. CASPT2 calculations gave a singlet–triplet energy gap of 16.6 kcal mol−1for1 N; thus, intersystem crossing of11Nto31Nis unlikely at ambient temperature, supporting the formation of31Nfrom T of1. Thus, sustainable synthetic methods for aryl azo‐dimers can be developed using the visible‐light irradiation of aryl azides to form triplet arylnitrenes.more » « less
-
Abstract The potential of an environmentally friendly and emerging chalcogenide perovskite CaZrSe3for thermoelectric applications is examined. The orthorhombic phase of CaZrSe3has an optimum band gap (1.35–1.40 eV) for single‐junction photovoltaic applications. The predictions reveal that CaZrSe3possesses an absorption coefficient of ≈4 × 105cm−1at photon energies of 2.5 eV with an early onset of optical absorption (≈0.2 eV) well below the optimum band gap. Seebeck coefficient,S, is inversely proportional to the carrier mobility as the calculated average effective mass for electrons is higher than for holes;p‐type doping enhances the electrical conductivity, σ. The electronic thermal conductivityκeremains low at all temperatures. The upper limit of the thermoelectric figure of merit (ZTe) attains ≈1.0 when doped at specific chemical potentials, while a high Seebeck coefficient contributes to the ZTe = 1.95 at 50 K forp‐type doping with 1018cm−3carrier concentration, demonstrating high thermoelectric efficiency.more » « less
-
Context.The study of quasar outflows is essential for understanding the connection between active galactic nuclei (AGN) and their host galaxies. We analyzed the VLT/UVES spectrum of quasar SDSS J0932+0840 and identified several narrow and broad outflow components in absorption, with multiple ionization species including Fe II. This places it among the rare class of outflows known as iron low-ionization broad absorption line outflows (FeLoBALs). Aims.We studied one of the outflow components to determine its physical characteristics by determining the total hydrogen column density, the ionization parameter, and the hydrogen number density. Through these parameters, we obtained the distance of the outflow from the central source, its mass outflow rate, and its kinetic luminosity, and we constrained the contribution of the outflow to the AGN feedback. Methods.We obtained the ionic column densities from the absorption troughs in the spectrum and used photoionization modeling to extract the physical parameters of the outflow, including the total hydrogen column density and ionization parameter. The relative population of the observed excited states of Fe IIwas used to model the hydrogen number density of the outflow. Results.We used the Fe IIexcited states to model the electron number density (ne) and hydrogen number density (nH) independently and obtainedne≃ 103.4cm−3andnH≃ 104.8cm−3. Our analysis of the physical structure of the cloud shows that these two results are consistent with each other. This places the outflow system at a distance of 0.7−0.4+0.9kpc from the central source, with a mass flow rate (Ṁ) of 43−26+65 M⊙yr−1and a kinetic luminosity (Ėk) of 0.7−0.4+1.1× 1043erg s−1. This is 0.5−0.3+0.7× 10−4of the Eddington luminosity (LEdd) of the quasar, and we thus conclude that this outflow is not powerful enough to contribute significantly toward AGN feedback.more » « less
-
Abstract We present the discovery of neutral gas detected in both damped Lyαabsorption (DLA) and Hi21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an Hibridge connecting two interacting dwarf galaxies (log (Mstar/M⊙) = 8.5 ± 0.2) that host az= 0.026 DLA with log[N(Hi)/cm−2] = 20.60 ± 0.05 toward the QSO J2339−5523 (zQSO= 1.35). At impact parameters ofd= 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≈0.05L*within at least Δv= ±300 km s−1andd≈ 350 kpc. The Hi21 cm emission is spatially coincident with the DLA at the 2σ–3σlevel per spectral channel over several adjacent beams. However, Hi21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratioTs/fc> 1880 K). Observations with VLT-MUSE demonstrate that theα-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≈10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf–dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and Hi21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.more » « less
