اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSignatures of tidal disruption in the Milky Way globular cluster NGC 6981 (M72)
104
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We study the outer regions of the Milky Way globular cluster NGC6981 from publicly available $BV$ photometry and new Dark Energy Camera (DECam) observations, both reaching nearly 4 mag below the cluster main sequence (MS) turnoff. While the $BV$ data sets reveal the present of extra-tidal features around the cluster, the much larger field of view of DECam observations allowed us to identify some other tidal features, which extend from the cluster toward the opposite direction to the Milky Way center. These cluster structural features arise from stellar density maps built using MS stars, once the cluster color-magnitude diagram was cleaned from the contamination of field stars. We also performed $N$-body simulations in order to help us to understand the spatial distribution of the extra-tidal debris. The outcomes reveal the presenceof long trailing and leading tails mostly parallel to the direction of the cluster velocity vector. We found that the cluster has lost most of its mass by tidal disruption during its perigalactic passages, that lasted nearly 20 Myr each. Hence, a decrease in the density of escaping stars near the cluster is expected from our $N$-body simulations, which in turn means that stronger extra-tidal features could be found out by exploring much larger areas around NGC6891.
قيم البحث
اقرأ أيضاً
We present results on the extra-tidal features of the Milky Way globular cluster NGC 7099, using deep gr photometry obtained with the Dark Energy Camera (DECam). We reached nearly 6 mag below the cluster Main Sequence (MS) turnoff, so that we dealt w
ith the most suitable candidates to trace any stellar structure located beyond the cluster tidal radius. From star-by-star reddening corrected color-magnitude diagrams (CMDs) we defined four adjacent strips along the MS, for which we built the respective stellar density maps, once the contamination by field stars was properly removed. The resulting field star cleaned stellar density maps show a short tidal tail and some scattered debris. Such extra-tidal features are hardly detected when much shallower Gaia DR2 data sets are used and the same CMD field star cleaning procedure is applied. Indeed, by using 2.5 magnitudes below the cluster MS turnoff as the faintest limit (G < 20.5 mag), cluster members turned out to be distributed within the clusters tidal radius, and some hints for field star density variations are found across a circle of radius 3.5deg centered on the cluster and with similar CMD features as cluster stars. The proper motion distribution of these stars is distinguishable from that of the cluster, with some superposition, which resembles that of stars located beyond 3.5deg from the cluster center.
We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widt
hs and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H] = -2.34$pm$0.05 dex (stat.) in accordance with previous studies. At a mean $alpha$-abundance of [(Mg,Si,Ca)/3 Fe] = 0.39$pm$0.03 dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter $alpha$-elements as well as the enhanced ratio [Zn/Fe] = 0.39 dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn point towards an enrichment history governed by the r-process with only little -if any- sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317.
We study the globular clusters (GCs) in the spiral galaxy NGC~5907 well-known for its spectacular stellar stream -- to better understand its origin. Using wide-field Subaru/Suprime-Cam $gri$ images and deep Keck/DEIMOS multi-object spectroscopy, we i
dentify and obtain the kinematics of several GCs superimposed on the stellar stream and the galaxy disk. We estimate the total number of globular clusters in NGC 5907 to be $154pm44$, with a specific frequency of $0.73pm0.21$. Our analysis also reveals a significant, new population of young star cluster candidates found mostly along the outskirts of the stellar disk. Using the properties of the stream GCs, we estimate that the disrupted galaxy has a stellar mass similar to the Sagittarius dwarf galaxy accreted by the Milky Way, i.e. $sim10^8~M_odot$.
The motion of the baryonic components of the Milky Way is governed by both luminous and dark matter content of the Galaxy. Thus, the dynamics of the Milky Way globular clusters can be used as tracers to infer the mass model of the Galaxy up to a larg
e radius. In this work, we use the directly observable line-of-sight velocities to test if the dynamics of the globular cluster population is consistent with an assumed axisymmetric gravitational potential of the Milky Way. For this, we numerically compute the phase space distribution of the globular cluster population where the orbits are either oriented randomly or co-/counter- rotating with respect to the stellar disk. Then we compare the observed position and line-of-sight velocity distribution of $sim$ 150 globular clusters with that of the models. We found that, for the adopted mass model, the co-rotating scenario is the favored model based on various statistical tests. We do the analysis with and without the GCs associated to the progenitors of early merger events. This analysis can be extended in the near future to include precise and copious data to better constrain the Galactic potential up to a large radius.
Milky Way globular clusters (MW GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-IR images and photometry from the VISTA Variables in the Via Lactea Extended S
urvey (VVVX) allow us to chart previously unexplored regions. Our long term aim is to complete the census of MW GCs. The immediate goals are to estimate the astrophysical parameters, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities and ages. We use the near-IR VVVX survey database, in combination with Gaia DR2 optical photometry, and with the Two Micron All Sky Survey (2MASS) photometry. We report the detection of a heretofore unknown Galactic Globular Cluster at $RA =$ 14:09:00.0; $DEC=-$65:37:12 (J2000). We calculate a reddening of $E(J-K_s)=(0.3pm 0.03)$ mag and an extinction of $A_{K_s}=(0.15pm 0.01)$ mag for this new GC. Its distance modulus and corresponding distance were measured as $(m-M)=(15.93pm0.03)$ mag and $D=(15.5pm1.0)$ kpc, respectively. We estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding $[Fe/H]=(-0.70pm0.2)$ dex and $t=(11.0pm1.0)$ Gyr. The mean GC PMs from Gaia are $mu_{alpha^ast}=(-4.68 pm 0.47 )$ mas $yr^{-1}$ and $mu_{delta}=(-1.34 pm 0.45)$ mas $yr^{-1}$. The total luminosity of our cluster is estimated to be $M_{Ks}=(-7.76pm 0.5)$ mag. We have found a new low-luminosity, old and metal-rich globular cluster, situated in the far side of the Galactic disk, at $R_{G}=11.2$ kpc from the Galactic centre, and at $z=1.0$ kpc below the plane. Interestingly, the location, metallicity and age of this globular cluster are coincident with the Monoceros Ring (MRi) structure.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
