اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSpatial Distributions of Young Stars
32
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We analyze the spatial distributions of young stars in Taurus-Auriga and Upper Sco as determined from the two-point correlation function (i.e. the mean surface density of neighbors). The corresponding power-law fits allow us to determine the fractal dimensions of each associations spatial distribution, measure the stellar velocity dispersions, and distinguish between the bound binary population and chance alignments of members. We find that the fractal dimension of Taurus is D~1.05, consistent with its filamentary structure. The fractal dimension of Upper Sco may be even shallower (D~0.7), but this fit is uncertain due to the limited area and possible spatially-variable incompleteness. We also find that random stellar motions have erased all primordial structure on scales of <0.07 degrees in Taurus and <1.7 degrees in Upper Sco; given ages of ~1 Myr and ~5 Myr, the corresponding internal velocity dispersions are ~0.2 km/s and ~1.0 km/s, respectively. Finally, we find that binaries can be distinguished from chance alignments at separations of <120 (17000 AU) in Taurus and 75 (11000 AU) in Upper Sco. The binary populations in these associations that we previously studied, spanning separations of 3-30, are dominated by binary systems. However, the few lowest-mass pairs (M_prim < 0.3 M_sun) might be chance alignments.
قيم البحث
اقرأ أيضاً
We investigate the relation of the stellar initial mass function (IMF) and the dense core mass function (CMF), using stellar masses and positions in 14 well-studied young groups. Initial column density maps are computed by replacing each star with a
model initial core having the same star formation efficiency (SFE). For each group the SFE, core model, and observational resolution are varied to produce a realistic range of initial maps. A clumpfinding algorithm parses each initial map into derived cores, derived core masses, and a derived CMF. The main result is that projected blending of initial cores causes derived cores to be too few and too massive. The number of derived cores is fewer than the number of initial cores by a mean factor 1.4 in sparse groups and 5 in crowded groups. The mass at the peak of the derived CMF exceeds the mass at the peak of the initial CMF by a mean factor 1.0 in sparse groups and 12.1 in crowded groups. These results imply that in crowded young groups and clusters, the mass distribution of observed cores may not reliably predict the mass distribution of protostars which will form in those cores.
The color-magnitude diagrams (CMDs) of young star clusters show that, particularly at ultraviolet wavelengths, their upper main sequences (MSs) bifurcate into a sequence comprising the bulk population and a blue periphery. The spatial distribution of
stars is crucial to understand the reasons for these distinct stellar populations. This study uses high-resolution photometric data obtained with the Hubble Space Telescope to study the spatial distributions of the stellar populations in seven Magellanic Cloud star clusters. The cumulative radial number fractions of blue stars within four clusters are strongly anti-correlated with those of the high-mass-ratio binaries in the bifurcated region, with negative Pearson coefficients < -0.7. Those clusters generally are young or in an early dynamical evolutionary stage. In addition, a supporting N-body simulation suggests the increasing percentage of blue-MS stars from the cluster centers to their outskirts may be associated with the dissolution of soft binaries. This study provides a different perspective to explore the MS bimodalities in young clusters and adds extra puzzles. A more comprehensive study combined with detailed simulations is needed in the future.
Thermonuclear supernovae (SNe), a subset of which are the highly important SNe Type,Ia, remain one of the more poorly understood phenomena known to modern astrophysics. In recent years, the single degenerate helium (He) donor channel, where a white d
warf star (WD) accretes He-rich matter from a hydrogen-depleted companion, has emerged as a promising candidate progenitor scenario for these events. An unresolved question in this scenario is the fate of the companion star, which would be evident as a runaway hot subdwarf (He sdO/B) in the aftermath of the SN event. Previous studies have shown that the kinematic properties of an ejected companion provide an opportunity to closer examination of the properties of an SN progenitor system. However, with the number of observed objects not matching predictions by theory, the viability of this mechanism is called into question. In this study, we first synthesize a population of companion stars ejected by the aforementioned mechanism, taking into account predicted ejection velocities, inferred population density in the Galactic (Gal.) mass distribution and subsequent kinematics in the Gal. potential. We then discuss the astrometric properties of this population. We present $10^{6}$ individual ejection trajectories, numerically computed with a newly developed, lightweight simulation framework. A peak in the density distribution for close objects is expected in the direction of the Gal. center. If the entire considered mass range is realized, the radial velocity distribution should show a peak at 500kms. If only close US,708 analogues are considered, there should be a peak at ($sim750-850$)kms. We show that the puzzling lack of confirmed surviving companion stars of thermonuclear SNe, though possibly an observation-related selection effect, may indicate a selection against high mass donors in the SD He donor channel. (-abridged-)
We study the spatial correlations between the H$alpha$ emission and different types of massive stars in two local galaxies, the Large Magellanic Cloud (LMC) and Messier 33. We compare these to correlations derived for core-collapse supernovae (CCSNe)
in the literature to connect CCSNe of different types with the initial masses of their progenitors and to test the validity of progenitor mass estimates which use the pixel statistics method. We obtain samples of evolved massive stars in both galaxies from catalogues with good spatial coverage and/or completeness, and combine them with coordinates of main-sequence stars in the LMC from the SIMBAD database. We calculate the spatial correlation of stars of different classes and spectral types with H$alpha$ emission. We also investigate the effects of distance, noise and positional errors on the pixel statistics method. A higher correlation with H$alpha$ emission is found to correspond to a shorter stellar lifespan, and we conclude that the method can be used as an indicator of the ages, and therefore initial masses, of SN progenitors. We find that the spatial distributions of type II-P SNe and red supergiants of appropriate initial mass ($gtrsim$9 $M_{odot}$) are consistent with each other. We also find the distributions of type Ic SNe and WN stars with initial masses $gtrsim$20 $M_{odot}$ consistent, while supergiants with initial masses around 15 $M_{odot}$ are a better match for type IIb and II-L SNe. The type Ib distribution corresponds to the same stellar types as type II-P, which suggests an origin in interacting binaries. On the other hand, we find that luminous blue variable stars show a much stronger correlation with H$alpha$ emission than do type IIn SNe.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
