Cold diffuse interstellar medium of Magellanic Clouds: II. Physical conditions from excitation of CI and H2_2

We present a comprehensive study of the excitation of CI fine-structure levels along 57 sight lines in the Large and Small Magellanic Clouds. The sight lines were selected by the detection of H$_2$ in FUSE spectra. Using archival HST/COS and HST/STIS spectra we detected absorption of CI fine-structure levels and measured their populations for 29 and 22 sight lines in the LMC and SMC, respectively. The CI column density ranges from $10^{13}$ to $10^{14}\,{\rm cm}^{-2}$ for the LMC and $10^{13}$ to $10^{15.4}\,{\rm cm}^{-2}$ for the SMC. We found excitation of CI fine-structure levels in the LMC and SMC to be 2-3 times higher than typical values in local diffuse ISM. Comparing excitation of both CI fine-structure levels and H$_2$ rotational levels with a grid of PDR Meudon models we find that neutral cold gas in the LMC and SMC is illuminated by stronger UV field than in local ISM ($\chi=5^{+7}_{-3}$ units of Mathis field for the LMC and $2^{+4}_{-1}$ for the SMC) and has on average higher thermal pressure ($\log p/k =4.2\pm0.4$ and $4.3\pm0.5$, respectively). Magellanic Clouds sight lines likely probe region near star-formation sites, which also affects the thermal state and CI/H$_2$ relative abundances. At the same time such high measurements of UV field are consistent with some values obtained at high redshifts. Together with low metallicities this make Magellanic Clouds to be an interesting test case to study of the central parts of high redshift galaxies.Comment: submitted to MNRA

Search for varying constants of nature from astronomical observation of molecules

The status of searches for possible variation in the constants of nature from astronomical observation of molecules is reviewed, focusing on the dimensionless constant representing the proton-electron mass ratio $\mu=m_p/m_e$. The optical detection of H$_2$ and CO molecules with large ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as the detection of H$_2$ with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope is discussed in the context of varying constants, and in connection to different theoretical scenarios. Radio astronomy provides an alternative search strategy bearing the advantage that molecules as NH$_3$ (ammonia) and CH$_3$OH (methanol) can be used, which are much more sensitive to a varying $\mu$ than diatomic molecules. Current constraints are $|\Delta\mu/\mu| < 5 \times 10^{-6}$ for redshift $z=2.0-4.2$, corresponding to look-back times of 10-12.5 Gyrs, and $|\Delta\mu/\mu| < 1.5 \times 10^{-7}$ for $z=0.88$, corresponding to half the age of the Universe (both at 3$\sigma$ statistical significance). Existing bottlenecks and prospects for future improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the International Space Science Institute, Bern 201

CUBES: a UV spectrograph for the future

In spite of the advent of extremely large telescopes in the UV/optical/NIR range, the current generation of 8-10m facilities is likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000, although a lower-resolution, sky-limited mode of R ~ 7,000 is also planned. CUBES will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the Phase B dedicated to detailed design and construction. First science operations are planned for 2028. In this paper, we briefly describe the CUBES project development and goals, the main science cases, the instrument design and the project organization and management

Magnetic, transport, and magnetotransport properties of the textured Fe3O4 thin films reactively deposited onto SiO2/Si

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The structural, magnetic, transport, and magnetotransport properties of Fe3O4 thin films with thicknesses from 38 nm to 95 nm are systematically investigated. The occurrence of the Verwey transition in these films at a temperature of about 120 K is established. It is found that the temperature dependences of the magnetic moment have a feature near 40 K, which can be attributed to the multiferroic phase. According to the X-ray diffraction data, the film structure represents a (001) texture. As was established using transmission electron microscopy, the height and width of texture crystallites increase with film thickness. Analysis of the temperature dependences of the resistivity showed that the dominant carrier transport mechanism in the films is thermoactivated tunneling. The thermoactivation energy, along with the room-temperature resistivity, decreases with increasing film thicknesses, which is most likely related to the variation in the crystallite size, especially in the crystallite width. The field dependence of magnetoresistance behaves similarly over the entire temperature range and has a positive MR peak in weak fields, which is related to spin-dependent tunneling through Fe3O4 grains and antiferromagnetically coupled antiphase boundaries

Magnetic, transport, and magnetotransport properties of the textured Fe3O4 thin films reactively deposited onto SiO2/Si

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The structural, magnetic, transport, and magnetotransport properties of Fe3O4 thin films with thicknesses from 38 nm to 95 nm are systematically investigated. The occurrence of the Verwey transition in these films at a temperature of about 120 K is established. It is found that the temperature dependences of the magnetic moment have a feature near 40 K, which can be attributed to the multiferroic phase. According to the X-ray diffraction data, the film structure represents a (001) texture. As was established using transmission electron microscopy, the height and width of texture crystallites increase with film thickness. Analysis of the temperature dependences of the resistivity showed that the dominant carrier transport mechanism in the films is thermoactivated tunneling. The thermoactivation energy, along with the room-temperature resistivity, decreases with increasing film thicknesses, which is most likely related to the variation in the crystallite size, especially in the crystallite width. The field dependence of magnetoresistance behaves similarly over the entire temperature range and has a positive MR peak in weak fields, which is related to spin-dependent tunneling through Fe3O4 grains and antiferromagnetically coupled antiphase boundaries