Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCorrelation between UV resilience and wavelength of narrow DIBs
195
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Carriers of diffuse interstellar bands (DIBs) still need to be identified. In a recent paper, we reported a correlation between the DIB wavelength and the apparent UV resilience (or boost) of their carriers. We proposed that this might be an indication of the important role of conjugated elongated molecules among the DIB carriers. The aim of this paper is to further understand the origin of this correlation. The analysis of 509 optical DIBs on the lines of sight of HD 183143 and/or HD 204827 reported in the literature shows that this correlation mainly implies the 386 narrow DIBs with a band width < 1.1 A, which include most of the identified DIBs of the C2 and zeta families, while the majority of the 123 broader DIBs, including the identified sigma DIBs, do not display such a correlation. We present a possible origin of this correlation from very strong bands of large conjugated elongated molecules, such as carbon chains, polyacenes, or other catacondensed polycyclic aromatic hydrocarbons. The total amount of carbon contained in all the carriers of these narrow DIBs is a very small fraction of the interstellar carbon if their oscillator strengths are <~1. The amount of carbon locked in the carriers of the broader DIBs is higher, especially if their oscillator strengths are significantly weaker.
rate research
Read More
The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disk of a supermassive black hole (SMBH) are expected to produce correlated flux variations in UV and optical bands. Recent work has further argued that binary quasars should exhibit strongly correlated UV and optical periodicities. Strong UV-optical correlations have indeed been established in small samples of up to approximately 30 quasars with well-sampled light curves, and have extended the bluer-when-brighter trend previously found within the optical bands. Here we further test the nature of quasar variability by examining the observed-frame UV-optical correlations in a large sample of 1,315 bright quasars with overlapping UV and optical light curves for the Galaxy Evolution Explorer (GALEX) and the Catalina Real-time Transient Survey (CRTS), respectively. We find that strong correlations exist in this much larger sample, but we rule out, at approximately 95% confidence, the simple hypothesis that the intrinsic UV and optical variations of all quasars are fully correlated. Our results therefore imply the existence of physical mechanism(s) that can generate uncorrelated optical and UV flux variations.
Ultraviolet photodesorption of molecules from icy interstellar grains can explain observations of cold gas in regions where thermal desorption is negligible. This non-thermal desorption mechanism should be especially important where UV fluxes are high. N2 and O2 are expected to play key roles in astrochemical reaction networks, both in the solid state and in the gas phase. Measurements of the wavelength-dependent photodesorption rates of these two infrared-inactive molecules provide astronomical and physical-chemical insights into the conditions required for their photodesorption. Tunable radiation from the DESIRS beamline at the SOLEIL synchrotron in the astrophysically relevant 7 to 13.6 eV range is used to irradiate pure N2 and O2 thin ice films. Photodesorption of molecules is monitored through quadrupole mass spectrometry. Absolute rates are calculated by using the well-calibrated CO photodesorption rates. Strategic N2 and O2 isotopolog mixtures are used to investigate the importance of dissociation upon irradiation. N2 photodesorption mainly occurs through excitation of the b^1Pi_u state and subsequent desorption of surface molecules. The observed vibronic structure in the N2 photodesorption spectrum, together with the absence of N3 formation, supports that the photodesorption mechanism of N2 is similar to CO, i.e., an indirect DIET (Desorption Induced by Electronic Transition) process without dissociation of the desorbing molecule. In contrast, O2 photodesorption in the 7 - 13.6 eV range occurs through dissociation and presents no vibrational structure. Photodesorption rates of N2 and O2 integrated over the far-UV field from various star-forming environments are lower than for CO. Rates vary between 10E-3 and 10E-2 photodesorbed molecules per incoming photon.
We present a detailed study of 11 narrow-line Seyfert 1 galaxies (NLS1s) from the Six-degree Field Galaxy Survey (6dFGS) that both have optical and X-ray spectroscopic observations. There are five complex NLS1s (C-NLS1s) and six simple NLS1s (S-NLS1s). We propose a possible correlation between [O III] line asymmetry and X-ray complexity. The outflow or wind from the inner accretion disk is commonly present in NLS1s and mostly directed along the system axis. In C-NLS1s only weak wind effects are measured, the X-ray spectral complexity might be caused by the presence of ionized material in the wind. On the contrary, the wind in S-NLS1s is fast, the ionized material could be swept by such a strong wind, thus the complex feature is missing which results in a simple X-ray spectrum. Furthermore, this outflow scenario seems to be an inclination effect. Since the speed of the wind is higher in a small inclination while lower in a large inclination, S-NLS1s might be sources viewed at small angles while C-NLS1s might be sources viewed at large angles.
We explore the properties of selected mid-ultraviolet (1900-3200 angstrom) spectroscopic indices of simple stellar populations (SSPs). We incorporate the high resolution UVBLUE stellar spectral library into an evolutionary population synthesis code, based on the most recent Padova isochrones. We analyze the trends of UV indices with respect to age and chemical composition. As a first test against observations, we compare our results with the empirical mid-UV spectral indices of Galactic globular clusters, observed with the International Ultraviolet Explorer (IUE). We find that synthetic indices exhibit a variety of properties, the main one being the slight age sensitivity of most of them for ages>2 Gyr. However, for high metallicity, two indices, Fe II 2332 and Fe II 2402, display a remarkably different pattern, with a sharp increase within the first two Gyr and, thereafter, a rapid decline. These indices clearly mark the presence of young (~1 Gyr) metal rich (Z > Z_sun) stellar populations. We complement existing UV indices of Galactic globular clusters with new measurements, and carefully identify a sub-sample of ten indices suitable for comparison with theoretical models. The comparison shows a fair agreement and, in particular, the strong trend of the indices with metallicity is well reproduced. We also discuss the main improvements that should be considered in future modelling concerning, among others, the effects of alpha-enhancement in the spectral energy distributions.
We compile a large sample of broad absorption lines (BAL) quasars with X-ray observations from the xmm archive data and Sloan Digital Sky Survey Data Release 5. The sample consists of 41 BAL QSOs. Among 26 BAL quasars detected in X-ray, spectral analysis is possible for twelve objects. X-ray absorption is detected in all of them. Complementary to that of citet{gall06} (thereafter G06), our sample spans wide ranges of both BALnicity Index (BI) and maximum outflow velocity (vmax). Combining our sample with G06s, we find very significant correlations between the intrinsic X-ray weakness with both BALnicity Index (BI) and the maximum velocity of absorption trough. We do not confirm the previous claimed correlation between absorption column density and broad absorption line parameters. We tentatively interpret this as that X-ray absorption is necessary to the production of the BAL outflow, but the properties of the outflow are largely determined by intrinsic SED of the quasars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
