Emission lines from Rydberg transitions are detected for the first time from a region close to the surface of Betelgeuse. The H30
We present observations of population anti-inversion in the 31− 40
- 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
-
more » « less
Abstract α line 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 H30α and the Rydberg combined line X30α are 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. X30α is located in a relatively smooth ring at a projected radius of 0.9× the optical photospheric radiusR ⋆, whereas H30α is 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 X30α emission 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
ABSTRACT Triplet arylnitrenes may provide direct access to aryl azo‐dimers, which have broad commercial applicability. Herein, the photolysis of
p ‐azidostilbene (1 ) in argon‐saturated methanol yielded stilbene azo‐dimer (2 ) through the dimerization of tripletp ‐nitrenostilbene (31N ). The formation of31N was verified by electron paramagnetic resonance spectroscopy and absorption spectroscopy (λ max ~ 375 nm) in cryogenic 2‐methyltetrahydrofuran matrices. At ambient temperature, laser flash photolysis of1 in methanol formed31N (λ max ~ 370 nm, 2.85 × 107 s−1). On shorter timescales, a transient absorption (λ max ~ 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 of11N to31N is unlikely at ambient temperature, supporting the formation of31N from 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 conductivityκe remains 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
Abstract We present the discovery of neutral gas detected in both damped Ly
α absorption (DLA) and Hi 21 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 Hi bridge connecting two interacting dwarf galaxies (log (M star/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 (z QSO= 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 Hi 21 cm emission is spatially coincident with the DLA at the 2σ –3σ level per spectral channel over several adjacent beams. However, Hi 21 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 ratioT s /f c > 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 Hi 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments. -
more » « less
Abstract Very young (
t ≲ 10 Myr) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar disks to the surface of the star. Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11–20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities ofn e = 1011–1012cm−3, and excitation temperatures that are inversely correlated with electron density (fromT ∼ 5000 K forn e ∼ 1012cm−3toT ∼ 12,500 K atn e ∼ 1011cm−3). These physical parameters are in good agreement with predictions from modeling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission-line sources in the APOGEE Data Release 17 data set.
