共查询到20条相似文献，搜索用时 15 毫秒
1.
S. G. Sichevskij 《Astrophysical Bulletin》2017,72(2):141-149
We describe Bayesian probabilistic approach to estimating the properties of stars and the interstellar extinction law based on photometric observations and using prior data about the parameters of the stars. The accuracy of the resulting estimates is analyzed in the case of SDSS and 2MASS surveys. We found that our estimates have no systematic deviations in the case of photometric accuracy typical of the surveys considered and errors of prior data of ΔT eff = ±150 K and Δlog g = ±0.5. Note that the error of the estimated interstellar extinction A 0 is of about 0. m 3, and the error of the R 0 estimate depends on extinction and is close 0.2 for moderate A0 values. The fractional error of the estimated stellar angular diameters is close to 10%. A possible application of our approach is to determine the dependence of interstellar extinction on distance using stars closely located in the same sky area. 相似文献
2.
S. G. Sichevskij 《Astrophysical Bulletin》2018,73(1):98-107
The feasibility of the determination of the physical conditions in star’s atmosphere and the parameters of interstellar extinction from broad-band photometric observations in the 300–3000 nm wavelength interval is studied using SDSS and 2MASS data. The photometric accuracy of these surveys is shown to be insufficient for achieving in practice the theoretical possibility of estimating the atmospheric parameters of stars based on ugriz and JHKs photometry exclusively because such determinations result in correlations between the temperature and extinction estimates. The uncertainty of interstellar extinction estimates can be reduced if prior data about the temperature are available. The surveys considered can nevertheless be potentially valuable sources of information about both stellar atmospheric parameters and the interstellar medium. 相似文献
3.
We present a new survey for Hα emission objects in the Circinus cloud complex and introduce an efficient photometric method for detecting Hα emission via observations in a narrow‐band filter. The observed flux is compared to a blackbody fit of the continuum. Our search strategy reveals 20 stars with strong Hα emission (EW > 10 Å), eight of them being new detections. All Hα stars display infrared excess corroborating their youth. On the other hand, the region contains a number of infrared excess objects that do not show Hα emission. Our results support the picture that accretion – as witnessed by Hα emission – is a highly variable phenomenon. Therefore, Hα surveys can only trace the temporarily active objects. In contrast, infrared excess is a more robust tracer that reveals most of the population of young stellar objects in a star forming region. Our analysis of the general stellar content of the region yields a reliable distance of 450 pc for the Circinus cloud. Moreover, we find a ratio of total‐to‐selective extinction of RV = 2.8 suggesting that smaller‐than‐normal dust grains may be present. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
The publication of large photometric surveys and the tools for the cross-identification of their objects open up a possibility
for obtaining multicolor photometry of hundreds of millions of objects. This, in turn, makes it possible not only to classify
the objects and determine their parameters, but also to measure the interstellar extinction towards them and produce an extinction
map for the Milky Way. The aim of this study is to develop a tool for the cross identification of objects in the most well-known
surveys and test it in several sky areas. To this end, we implemented an algorithm of fast positional matching of large astronomical
catalogs in small (up to one degree) sized areas with filtering of false identification. As a result, we drew in seven 0.1-degree
radius areas samples of objects from the DENIS, 2MASS, SDSS, GALEX, and UKIDSS surveys, and performed the cross-identification
of these surveys. We compiled the corresponding subcatalogs in the VO Table format. The tool developed as a result of this
work can be used to cross-identify objects in arbitrary sky areas for the further classification and determination of stellar
parameters, including the measurement of the amount of interstellar extinction. 相似文献
5.
Blue Supergiants (BSGs) are the brightest stars in the universe at visual light with absolute magnitudes up to M V =−10 mag. They are ideal stellar objects for the determination of extragalactic distances, in particular, because the perennial uncertainties troubling most of the other stellar distance indicators, interstellar extinction and metallicity, do not affect them. The quantitative spectral analysis of low resolution spectra of individual BSGs provides accurate stellar parameters and chemical composition, which are then used to determine accurate reddening and extinction from photometry for each individual object. Accurate distances can be determined from stellar gravities and effective temperatures using the “Flux Weighted Gravity–Luminosity Relationship (FGLR)”. 相似文献
6.
V. T. Doroshenko S. G. Sergeev Yu. S. Efimov S. Nazarov V. I. Pronik E. A. Sergeeva G. A. Sivtsov 《Astrophysics》2007,50(1):40-53
Observations with a matrix photometer are reported. The stellar magnitudes in the BVRcIc bands are estimated for 80 comparison
stars in the neighborhoods of 10 galaxies with active nuclei: 2 Seyfert galaxies, 4 quasars, and 4 BL Lac objects. The stellar
magnitudes of the observed stars range from 11 to 19m.5. For stars with magnitudes of 14–15m the typical photometric errors are 0m.011, 0m.008, 0m.006, and 0m.007 in the B, V, R, and I bands, respectively. The BVRI magnitudes for most of these stars were not known previously. 14′
× 14′ finding charts for these stars are included. These results can be used for differential BVRI photometry of active galactic
nuclei.
__________
Translated from Astrofizika, Vol. 50, No. 1, pp. 57–72 (February 2007). 相似文献
7.
John P. Blakeslee John R. Lucey Brian J. Barris Michael J. Hudson John L. Tonry 《Monthly notices of the Royal Astronomical Society》2001,327(3):1004-1020
We perform a series of comparisons between distance-independent photometric and spectroscopic properties used in the surface brightness fluctuation (SBF) and fundamental plane (FP) methods of early-type galaxy distance estimation. The data are taken from two recent surveys: the SBF Survey of Galaxy Distances and the Streaming Motions of Abell Clusters (SMAC) FP survey. We derive a relation between colour and Mg2 index using nearly 200 galaxies and discuss implications for Galactic extinction estimates and early-type galaxy stellar populations. We find that the reddenings from Schlegel et al. for galaxies with appear to be overestimated by per cent, but we do not find significant evidence for large-scale dipole errors in the extinction map. In comparison with stellar population models having solar elemental abundance ratios, the galaxies in our sample are generally too blue at a given Mg2 ; we ascribe this to the well-known enhancement of the α -elements in luminous early-type galaxies. We confirm a tight relation between stellar velocity dispersion σ and the SBF 'fluctuation count' parameter N¯ , which is a luminosity-weighted measure of the total number of stars in a galaxy. The correlation between N¯ and σ is even tighter than that between Mg2 and σ . Finally, we derive FP photometric parameters for 280 galaxies from the SBF survey data set. Comparisons with external sources allow us to estimate the errors on these parameters and derive the correction necessary to bring them on to the SMAC system. The data are used in a forthcoming paper, which compares the distances derived from the FP and SBF methods. 相似文献
8.
G. Baume † G. Carraro ‡ Y. Momany § 《Monthly notices of the Royal Astronomical Society》2009,398(1):221-232
We present optical ( UBVI C ) observations of a rich and complex field in the Galactic plane towards l ∼ 305° and b ∼ 0° . Our analysis reveals a significantly high interstellar absorption ( A V ∼ 10) and an abnormal extinction law in this line of sight. Availing a considerable number of colour combinations, the photometric diagrams allow us to derive new estimates of the fundamental parameters of the two open clusters Danks 1 and Danks 2. Due to the derived abnormal reddening law in this line of sight, both clusters appear much closer (to the Sun) than previously thought. Additionally, we present the optical colours and magnitudes of the WR 48a star, and its main parameters were estimated. The properties of the two embedded clusters, DBS2003 130 and 131, are also addressed. We identify a number of young stellar objects which are probable members of these clusters. This new material is then used to revisit the spiral structure in this sector of the Galaxy showing evidence of populations associated with the inner Galaxy Scutum-Crux arm. 相似文献
9.
2MASS is the most complete, homogeneous, and least contaminated catalog among the deep all-sky catalogs of stellar data produced to date. These qualities allow it to be successfully used not only for astrophysical studies, but also for solving various problems of all-sky astrometry and for operational support of automated telescopes. However, the lack of optical photometry in the catalog prevents its potential from being completely unveiled. To overcome this shortcoming, we have developed a procedure for transforming the 2MASS near-infrared magnitudes to optical magnitudes R J relative to the UCAC2 magnitudes R U . As a result of applying this procedure, all 2MASS objects have gotten optical magnitudes with effective wavelengths between the V and R bands of the Johnson system. The resulting transformation accuracy \(\varepsilon _{R_J } \) < 0 . m 5). We also give a brief overview of the present-day all-sky catalogs with emphasis on their photometric properties and completeness. 相似文献
10.
We present a software package developed for the automatic 4-D stellar parameterization. The package can be adopted to virtually
any multicolour photometric system. Procedure of simultaneous determination of T
eff, log g, [M/H] and E
B-V is very flexible and can be performed by applying various photometric parameters(magnitudes, colour indices etc.). Any changes
of the photometric systems, weighting schemes or parameterization criteria can be implemented easily.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
12.
Determination of Stellar Parameters with GAIA 总被引：1，自引：0，他引：1
C.A.L. Bailer-Jones 《Astrophysics and Space Science》2002,280(1-2):21-29
The GAIA Galactic survey satellite will obtain photometry in 15 filters of over 109 stars in our Galaxy across a very wide range of stellar types. No other planned survey will provide so much photometric information
on so many stars. I examine the problem of how to determine fundamental physical parameters (T
eff, log g, [Fe/H] etc.) from these data. Given the size, multidimensionality and diversity of this dataset, this is a challenging task
beyond any encountered so far in large-scale stellar parametrization. I describe the problems faced (initial object identification,
interstellar extinction, multiplicity, missing data etc.) and present a framework in which they can be addressed. A probabilistic
approach is advocated on the grounds that it can take advantage of additional information (e.g. priors and data uncertainties)
in a consistent and useful manner, as well as give meaningful results in the presence of poor or degenerate data. Furthermore,
I suggest an approach to parametrization which can use the other information GAIA will acquire, in particular the parallax,
which has not previously been available for large-scale multidimensional parametrization. Several of the problems identified
and ideas suggested will be relevant to other large surveys, such as SDSS, DIVA,FAME, VISTA and LSST, as well as stellar parametrization
in a virtual observatory.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
We have measured the interstellar extinction in the region of ultradeep Galactic-field observations by the Chandra telescope (l II, b II) ≈ 0.1–1.42 using photometric data from the 2MASS infrared allsky survey. The angular resolution of our interstellar extinction map is 1′.8. We show that the interstellar extinction has a minimum, A V ～ 3.4, near the center of the Chandra field of view and increases to A V ～ 5.8–6 at the edge of the field of view. In addition, we show that the bulk of the extinction is gained in the Galactic disk and is approximately the same for all bulge stars. Our results will be subsequently used to process the Chandra data and to estimate the properties of the stellar population in this region. 相似文献
14.
S. G. Sichevskij 《Astrophysical Bulletin》2017,72(1):51-57
Based on the spectral observations of the LAMOST (DR2) survey, the radii, masses, and luminosities of 700 481 stars were estimated. These stars belong to spectral types A, F, G, and K, and have metallicities between ?0.845 and 0.0. To determine the properties of the stars, we used up-to-date models of the stellar interior structure, computed with account for the stellar evolution rate and the initial mass function. The use of evolutionary estimates for two types of stars—with and without rotation—allowed us to account for the uncertainty associated with the lack of data on the rotation velocity of the stars under consideration. The obtained stellar radii, together with the photometric estimates of interstellar extinction and angular diameters can be used to study the dependence of interstellar extinction on distance as well as to estimate the stellar distances. 相似文献
15.
K.G. Noeske L.M. Cairós P. Papaderos J.M. Vílchez K.J. Fricke 《Astrophysics and Space Science》2001,276(2-4):901-908
We are currently analysing image data for a large sample of blue compact dwarf galaxies (BCDs), obtained in multiple optical
broad- and narrow-band filters. We present preliminary results of a multi-band analysis of two typical BCDs, Mrk 5 and I Zw
123, for which surface-brightness profiles, colour profiles, colour maps and Hα equivalent-width maps have been derived. We demonstrate how a combination of these different processing methods allows a
separate analysis of the young and old stellar populations with respect to their colours and spatial distributions. By comparing
the derived colours with the predictions of evolutionary synthesis models, we estimate ages of the distinct stellar populations.
The surface-brightness profiles of Mrk 5 show an exponential decay at large photometric radii, with slopes typically found
for BCDs. In the case of the very compact object I Zw 123, the surface-brightness profile of the underlying stellar component
can be described either by an exponential or an R
1/4 law. We discuss briefly how noise effects can influence the intrinsic slope of surface brightness profiles at low surface-brightness
levels. For compact objects with extended starbursts, the study of the underlying stellar population can thereby be rendered
difficult.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
17.
We propose a multicomponent analysis of starburst galaxies, based on a model that takes into account the young and evolved stellar components and the gas emission, with their respective extinction, in the frame of a coherent dust distribution pattern. Near-IR signatures are preferentially investigated, in order to penetrate as deep as possible into the dusty starburst cores. We computed the 1.4-2.5 μm spectra of synthetic stellar populations evolving through strong, short timescale bursts of star formation (continuum and lines, R ? 500). The evolution model is specifically sensitive to cool stellar populations (AGB and red supergiant stars). It takes advantage of the stellar library of Lançon & Rocca-Volmerange (1992) [A&ASS, 96, 593], observed with the same instrument (FTS/CFHT) as the analysed galaxy sample, so that the instrumental effects are minimised. The main near-IR observable constraints are the molecular signatures of CO and H2O and the slope of the continuum, observed over a range exceptionally broad for spectroscopic data. The H - K colour determined from the spectra measures the intrinsic stellar energy distribution but also differential extinction, which is further constrained by optical emission line ratios. Other observational constraints are the near-IR emission lines (Brγ, He I 2.06 μm, [Fe II] 1.64 μm, H2 2.12 μm) and the far-IR luminosity. The coherence of the results relies on the interpretation in terms of stellar populations from which all observable properties are derived, so that the link between the various wavelength ranges is secured. The luminosity LK is used for the absolute calibration.We apply this approach to the typical spectrum of the core of NGC 1614. Consistent solutions for the starburst characteristics (star-formation rate, IMF, burst age, morphology) are found and the role of each observational constraint in deriving satisfactory models is extensively discussed. The acceptable contamination of the K band light by the underlying population amounts ≥ 15% even through a 5 arcsec aperture. The model leads to a limit on the direct absorption of Lyman continuum photons by dust situated inside the ionised areas, which in turn, with standard gas-to-dust ratios, translates into small characteristic sizes for the individual coexisting H II regions of the massive starburst area (clusters containing ∼ 102 ionising stars). We show that room is left for IMFs extending to 120 M⊙, rather than truncated at ∼ 60 M⊙ as most conservative studies conclude. High internal velocity dispersions (≥ 20 km s−1) are then needed for the H II regions. An original feature of this work is to base the analysis of near-infrared spectral galaxy observations on a large wavelength range, using models constructed with spectral stellar data observed with the same instrument. However a broader use of this spectral evolution model on other spectral or photometric data samples is possible if the spectral resolution of the model is adapted to observations or if colours are derived from the energy distributions.Catherine J. Cesarsky 相似文献
18.
与传统CCD (Charge Coupled Device)相机相比, s COMS (scientific Complementary Metal Oxide Semiconductor)相机被广泛装备于超大天区巡天设备,与传统CCD相机不同的是sCMOS相机采用卷帘式快门,因此对其进行测光精度的分析工作是很有意义的.首先,将s CMOS相机拍摄的图像与UCAC2 (The Second U.S. Naval Observatory CCD Astrograph Catalog)星表进行匹对,识别图像中的UCAC2标准星.接着对图中的标准星进行测光并提取测光数据进行最小二乘直线拟合,获得了相应的系统转换系数并得到仪器星等至标准星等的转换公式.然后,将转化后的仪器星等和标准星等做差并计算相应的均方根误差.最后,利用计算得到的均方根误差评估sCMOS相机的测光精度,并将标准星按星等划分后,分析了相应的测光误差.计算结果表明在标准测光夜测量亮度亮于14等的星时,测光精度优于0.15 mag.通过实测精度分析可知卷帘快门sCOMS相机具有较高的测光精度,基本满足空间碎片巡天观测的要求. 相似文献
19.
E. M. Edmondson L. Miller C. Wolf 《Monthly notices of the Royal Astronomical Society》2006,371(4):1693-1704
The next generation of weak gravitational lensing surveys are capable of generating good measurements of cosmological parameters, provided that, amongst other requirements, adequate redshift information is available for the background galaxies that are measured. It is frequently assumed that photometric redshift techniques provide the means to achieve this. Here, we compare Bayesian and frequentist approaches to photometric redshift estimation, particularly at faint magnitudes. We identify and discuss the biases that are inherent in the various methods, and describe an optimum Bayesian method for extracting redshift distributions from photometric data. 相似文献
20.
V. P. Arkhipova N. P. Ikonnikova G. V. Komissarova V. F. Esipov 《Astronomy Letters》2002,28(11):778-782
We present our photometric and spectroscopic observations of the hot emission-line high-latitude (b=+64°) star discovered by Haro. The star exhibited no light variability during 1993–2001. Based on our observations and on the detailed study of the star by Herbig (1992), we improved its parameters, T=22000 K and logg=4.2, and inferred its evolutionary status. We show that Haro’s star does not belong to the class of protoplanetary objects but is most likely a hot subdwarf of the Galactic halo with an emission-line spectrum formed in the outer layers of the star or in its stellar wind. 相似文献