اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEclipsing binaries in the Magellanic Clouds. uvby CCD light curves and photometric analyses for HV982 (LMC), HV12578 (LMC), HV1433 (SMC), and HV11284 (SMC)
190
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present new accurate CCD uvby light curves for the LMC eclipsing binaries HV982 and HV12578, and for the SMC systems HV1433 and HV11284 obtained at the Danish 1.5m telescope at ESO, La Silla. The light curves were derived from DoPHOT photometry, and typical accuracies are between 0.007 and 0.012 mag per point. Standard uvby indices have also been established for each binary, primarily for determination of interstellar reddening and absorption. For HV982 and HV12578, accurate photometric elements have been established. Both systems consist of two detached components of comparable sizes in an eccentric orbit. Adopting the spectroscopic elements given by Fitzpatrick et al. 2002 for HV982, we derive absolute dimensions of its components which agree well with their results. A distance modulus of V_0-M_V = 18.63 +/- 0.08 is obtained, corresponding to a distance of 52.6 +/- 2.0 kpc, which is in formal agreement with (although slightly larger than) their determination. HV1433 and HV11284 both consist of two rather close, deformed and quite different stars. As the mass ratios between the components (and their rotation rates) are not known, definitive photometric elements can not yet be obtained, but we present a sample of possible photometric solutions. In a series of forthcoming papers we will combine our uvby observations with high-dispersion spectra from the UVES spectrograph on the ESO Very Large Telescope (VLT) and present absolute dimensions, chemical abundances and distances for selected LMC and SMC systems, including HV12578 and refined results for HV982.
قيم البحث
اقرأ أيضاً
We present an analysis of the stellar kinematics of the Large Magellanic Cloud based on ~5900 new and existing velocities of massive red supergiants, oxygen-rich and carbon-rich AGB stars, and other giants. After correcting the line-of-sight velociti
es for the LMCs space motion and accounting for asymmetric drift in the AGB population, we derive a rotation curve that is consistent with all of the tracers used, as well as that of published HI data. The amplitude of the rotation curve is v_0=87+/-5 km s^-1 beyond a radius R_0=2.4+/-0.1 kpc, and has a position angle of the kinematic line of nodes of theta=142 degrees +/-5 degrees. By examining the outliers from our fits, we identify a population of 376 stars, or >~5% of our sample, that have line-of-sight velocities that apparently oppose the sense of rotation of the LMC disk. We find that these kinematically distinct stars are either counter-rotating in a plane closely aligned with the LMC disk, or rotating in the same sense as the LMC disk, but in a plane that is inclined by 54 degrees +/- 2 degrees to the LMC. Their kinematics clearly link them to two known HI arms, which have previously been interpreted as being pulled out from the LMC. We measure metallicities from the Ca triplet lines of ~1000 LMC field stars and 30 stars in the kinematically distinct population. For the LMC field, we find a median [Fe/H]=-0.56 +/- 0.02 with dispersion of 0.5 dex, while for the kinematically distinct stars the median [Fe/H] is -1.25 +/- 0.13 with a dispersion of 0.7 dex. The metallicity differences provide strong evidence that the kinematically distinct population originated in the SMC. This interpretation has the consequence that the HI arms kinematically associated with the stars are likely falling into the LMC, instead of being pulled out.
We present a measurement of the systemic proper motion of the Small Magellanic Cloud (SMC) made using the Advanced Camera for Surveys (ACS) on the textit{Hubble Space Telescope} (textit{HST}). We tracked the SMCs motion relative to 4 background QSOs
over a baseline of approximately 2 years. The measured proper motion is : $mu_W = -1.16 pm 0.18 masyr, mu_N = -1.17 pm 0.18 masyr$. This is the best measurement yet of the SMCs proper motion. We combine this new result with our prior estimate of the proper motion of the Large Magellanic Cloud (LMC) from the same observing program to investigate the orbital evolution of both Clouds over the past 9 Gyr. The current relative velocity between the Clouds is $105 pm 42 kms$. Our investigations of the past orbital motions of the Clouds in a simple model for the dark halo of the Milky Way imply that the Clouds could be unbound from each other. However, our data are also consistent with orbits in which the Clouds have been bound to each other for approximately a Hubble time. Smaller proper motion errors and better understanding of the LMC and SMC masses would be required to constrain their past orbital history and their bound vs. unbound nature unambiguously. The new proper motion measurements should be sufficient to allow the construction of improved models for the origin and properties of the Magellanic Stream. In turn, this will provide new constraints on the properties of the Milky Way dark halo.
We present an exhaustive, quantitative comparison of all of the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior of Milky Way extinction curves. The R_V dependent CCM relati
onship and the sample of extinction curves used to derive this relationship is used to describe the general behavior of Milky Way extinction curves. The ultraviolet portion of the SMC and LMC extinction curves are derived from archival IUE data, except for one new SMC extinction curve which was measured using HST/STIS observations. The optical extinction curves are derived from new (for the SMC) and literature UBVRI photometry (for the LMC). The near-infrared extinction curves are calculated mainly from 2MASS photometry supplemented with DENIS and new JHK photometry. For each extinction curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust column as the extinction curve. We compare the properties of the SMC and LMC extinction curves with the CCM relationship three different ways: each curve by itself, the behavior of extinction at different wavelengths with R_V, and behavior of the extinction curve FM fit parameters with R_V. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship, but majority of the LMC and all of the SMC curves do not follow the CCM relationship. For the first time, we find that the CCM relationship seems to form a bound on the properties of all of the LMC and SMC extinction curves. This result strengthens the picture of dust extinction curves exhibit a continuum of properties between those found in the Milky Way and the SMC Bar. (abridged)
Based on their stellar parameters and the presence of a mid-IR excess due to circumstellar dust, RV Tauri stars have been classified as post-AGB stars. Our recent studies, however, reveal diverse SEDs among RV Tauri stars, suggesting they may occupy
other evolutionary channels as well. The aim of this paper is to present the diverse SED characteristics of RV Tauri stars and investigate their evolutionary nature as a function of their SEDs. We carried out a systematic study of RV Tauri stars in the SMC and LMC because of their known distances and hence luminosities. Their SEDs were classified in three groups: dusty (disc-type), non-dusty (non-IR) and uncertain. A period-luminosity- colour (PLC) relation was calibrated. The luminosities from the PLC were complemented with the ones found using their SEDs and the stars were placed on the HR-diagram. The four main results from this study are: 1) RV Tauri stars with a clear IR-excess have disc-type SEDs, which indicates that the dust is trapped in a stable disc. Given the strong link between disc-type SEDs and binarity in the Galaxy, we postulate that these are binaries as well. These cover a range of luminosities and we argue that the more luminous ones are post-AGB stars while the lower luminosity ones are likely post-Red Giant Branch (post-RGB) stars. 2) Two of these objects have variable mean brightness with periods of 916 and 850 days, respectively, caused by variable extinction during orbital motion. 3) The non-dusty RV Tauri stars and the objects with an uncertain SED evolve such that the circumstellar dust has dispersed. If they are single stars, they are post-AGB objects of low initial mass ($<$ 1.25 M$_odot$), while if they are binaries, the low-luminosity part of the sample are likely post-RGB stars. 4) We find that RV Tauri stars with dust are on average more luminous than the rest of the sample.
We present an analysis of the spatial distribution of various stellar populations within the Large and Small Magellanic Clouds. We use optically selected stellar samples with mean ages between ~9 and ~1000 Myr, and existing stellar cluster catalogues
to investigate how stellar structures form and evolve within the LMC/SMC. We use two statistical techniques to study the evolution of structure within these galaxies, the $Q$-parameter and the two-point correlation function (TPCF). In both galaxies we find the stars are born with a high degree of substructure (i.e. are highly fractal) and that the stellar distribution approaches that of the background population on timescales similar to the crossing times of the galaxy (~80/150 Myr for the SMC/LMC respectively). By comparing our observations to simple models of structural evolution we find that popping star clusters do not significantly influence structural evolution in these galaxies. Instead we argue that general galactic dynamics are the main drivers, and that substructure will be erased in approximately the crossing time, regardless of spatial scale, from small clusters to whole galaxies. This can explain why many young Galactic clusters have high degrees of substructure, while others are smooth and centrally concentrated. We conclude with a general discussion on cluster infant mortality, in an attempt to clarify the time/spatial scales involved.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
