اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدInterstellar reddening towards six small areas in Puppis-Vela
122
0
0.0
(
0
)
تأليف
G. A. P. Franco
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We investigate the distribution of the interstellar dust towards six small volumes of the sky in the region of the Gum nebula. New high-quality four-colour uvby and Hbeta Stromgren photometry obtained for 352 stars in six selected areas of Kapteyn, complemented with data obtained in a previous investigation for two of these areas, were used to estimate the colour excess and distance to these objects. The obtained colour excess versus distance diagrams, complemented with other information, when available, were analysed in order to infer the properties of the interstellar medium permeating the observed volumes. On the basis of the overall standard deviation in the photometric measurements, we estimate that colour excesses and distances are determined with an accuracy of 0.010 mag and better than 30%, respectively, for a sample of 520 stars. A comparison with 37 stars in common with the new Hipparcos catalogue attests to the high quality of the photometric distance determination. The obtained colour excess versus distance diagrams testify to the low density volume towards the observed lines-of-sight. Very few stars out to distances of 1 kpc from the Sun have colour excesses larger than E(b-y) = 0.1 mag. In spite of the low density character of the interstellar medium towards the Puppis-Vela direction, the obtained reddening as a function of the distance indicates that two or more interstellar structures are crossed towards the observed lines-of-sight. One of these structures may be associated with the very low density wall of the Local Cavity, which has a distance of 100-150 pc from the Sun. Another structure might be related to the Gum nebula, and if so, its front face would be located at about 350 pc from the Sun.
قيم البحث
اقرأ أيضاً
Ultra-high spectral resolution observations of time-varying interstellar absorption towards {kappa} Vel are reported, using the Ultra-High Resolution Facility on the Anglo-Australian Telescope. Detections of interstellar Ca I, Ca II, K I, Na I and CH
are obtained, whilst an upper limit on the column density is reported for C_2. The results show continued increases in column densities of K I and Ca I since observations ~ 4 yr earlier, as the transverse motion of the star carried it ~ 10 AU perpendicular to the line of sight. Line profile models are fitted to the spectra and two main narrow components (A & B) are identified for all species except CH. The column density N(K I) is found to have increased by 82 +10-9 % between 1994 and 2006, whilst N(Ca I) is found to have increased by 32 +- 5 % over the shorter period of 2002-2006. The line widths are used to constrain the kinetic temperature to T_k,A < 671 +18-17 K and T_k,B < 114 +15-14 K. Electron densities are determined from the Ca I / Ca II ratio, which in turn place lower limits on the total number density of n_A > 7 * 10^3 cm^-3 and n_B > 2 * 10^4 cm^-3. Calcium depletions are estimated from the Ca I / K I ratio. Comparison with the chemical models of Bell et al. (2005) confirms the high number density, with n = 5 * 10^4 cm^-3 for the best-fitting model. The first measurements of diffuse interstellar bands (DIBs) towards this star are made at two epochs, but only an upper limit of < 40 % is placed on their variation over ~ 9 years. The DIBs are unusually weak for the measured E(B-V) and appear to exhibit similar behaviour to that seen in Orion. The ratio of equivalent widths of the {lambda}5780 to {lambda}5797 DIBs is amongst the highest known, which may indicate that the carrier of {lambda}5797 is more sensitive to UV radiation than to local density.
It is well known that interstellar spectral features correlate with color excess E(B$-$V). This suggests that measuring intensities of these features allows one to estimate reddening of stars. The aim of this paper is to check how tight intensities o
f interstellar diffuse bands (DIBs)are related to the amount of extinction, measured using E(B$-$V). We have measured equivalent widths of the strongest DIBs (centered at $lambdalambda$ 5780.6, 5797.0, 6196.0, 6379.3, 6613.5, and 8620.7 A), as well as of CH (near 4300.3 A) and CH$^+$ (near 4232.5 A) in high resolution, high S/N ratio echelle spectra from several spectrographs. The equivalent widths of the 8620 DIB in noisy spectra were measured using a template, which was constructed using the high quality spectrum of BD+40 4220. DIB relations with the color excess in the range 0.1--2.0 mag were examined. Our careful analysis demonstrates that all the above mentioned interstellar spectral features (except, perhaps, 6379 DIB) do correlate with E(B$-$V) relatively tightly (with the Pearsons correlation coefficient of 0.8+). Moreover, the observed scatter is apparently not caused by measurement errors but is of physical origin. We present several examples where the strength ratios of a DIB/molecule to E(B$-$V) are different than the average.
We have investigated the interstellar reddening law of young open clusters within 3kpc from the Sun using optical, near-IR 2MASS, and Spitzer IRAC data. The total-to-selective extinction ratio Rv of 162 young open clusters (log t{age} <= 7.3) listed
in the open cluster database WEBDA is determined from the color excess ratios. The young open clusters in the Sgr-Car arm show a relatively higher $R_V$, those in the Per arm and in the Cygnus region of the local arm show a relatively smaller value, and those in the Mon-CMa region of the local arm show a normal value (Rv ~ 3.1).
Using high-resolution (~85000) and high signal-to-noise ratio (~200) optical spectra acquired with the European Southern Observatory Ultraviolet and Visual Echelle Spectrograph, we have determined the interstellar column densities of C2 for six Galac
tic lines of sight with E(B- V) ranging from 0.33 to 1.03. For our purposes, we identified and measured absorption lines belonging to the (1, 0), (2, 0) and (3, 0) Phillips bands A1{Pi}u-X1{Sigma}+g. We report on the identification of a few lines of the C2 (4, 0) Phillips system towards HD 147889. The curve-of-growth method is applied to the equivalent widths to determine the column densities of the individual rotational levels of C2. The excitation temperature is extracted from the rotational diagrams. The physical parameters of the intervening molecular clouds (e.g. gas kinetic temperatures and densities of collision partners) were estimated by comparison with the theoretical model of excitation of C2.
We present new three-dimensional (3D) interstellar dust reddening maps of the Galactic plane in three colours, E(G-Ks), E(Bp-Rp) and E(H-Ks). The maps have a spatial angular resolution of 6 arcmin and covers over 7000 deg$^2$ of the Galactic plane fo
r Galactic longitude 0 deg $<$ $l$ $<$ 360 deg and latitude $|b|$ $<$ $10$ deg. The maps are constructed from robust parallax estimates from the Gaia Data Release 2 (Gaia DR2) combined with the high-quality optical photometry from the Gaia DR2 and the infrared photometry from the 2MASS and WISE surveys. We estimate the colour excesses, E(G-Ks), E(Bp-Rp) and E(H-Ks), of over 56 million stars with the machine learning algorithm Random Forest regression, using a training data set constructed from the large-scale spectroscopic surveys LAMOST, SEGUE and APOGEE. The results reveal the large-scale dust distribution in the Galactic disk, showing a number of features consistent with the earlier studies. The Galactic dust disk is clearly warped and show complex structures possibly spatially associated with the Sagittarius, Local and Perseus arms. We also provide the empirical extinction coefficients for the Gaia photometry that can be used to convert the colour excesses presented here to the line-of-sight extinction values in the Gaia photometric bands.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
