اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe Dispersed Young Population in Orion
319
0
0.0
(
0
)
تأليف
Cesar Briceno
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The Orion OB1 Association, at a distance of roughly 400 pc and spanning over ~200 deg^2 on the sky, is one of the largest and nearest OB associations. With a wide range of ages and environmental conditions, Orion is an ideal laboratory for investigating fundamental questions related to the birth of stars and planetary systems. This rich region exhibits all stages of the star formation process, from very young, embedded clusters, to older, fully exposed young stars; it also harbors dense clusters and widely spread populations in vast, low stellar density areas. This review focuses on the later, namely, the low-mass (M ~< 2 Mo), pre-main sequence population spread over wide spatial scales in Orion OB1, mostly in the off-cloud areas. As ongoing studies yield more complete censa it becomes clearer that this distributed or non-clustered population, is as numerous as that located in the molecular clouds; modern studies of star formation in Orion would be incomplete if they did not include this widely spread population.
قيم البحث
اقرأ أيضاً
We present the results of the SDSS APOGEE INfrared Spectroscopy of Young Nebulous Clusters program (IN-SYNC) survey of the Orion A molecular cloud. This survey obtained high resolution near infrared (NIR) spectroscopy of about 2700 young pre-main seq
uence stars throughout the region, acquired across five distinct fields spanning 6deg field of view (FOV). With these spectra, we have measured accurate stellar parameters (T_eff, log g, v sin i) and extinctions, and placed the sources in the Hertzsprung-Russel Diagram (HRD). We have also extracted radial velocities for the kinematic characterization of the population. We compare our measurements with literature results for a sub-sample of targets in order to assess the performances and accuracy of the survey. Source extinction shows evidence for dust grains that are larger than those in the diffuse interstellar medium (ISM): we estimate an average R_V=5.5 in the region. Importantly, we find a clear correlation between HRD inferred ages and spectroscopic surface-gravity inferred ages. This clearly indicates a real spread of stellar radii at fixed temperature, and together with additional correlations with extinction and with disk presence, strongly suggests a real spread of ages large than a few Myr. Focussing on the young population around NGC1980 iota Ori, which has previously been suggested to be a separate, foreground, older cluster, we confirm its older (5Myr) age and low A_V, but considering that its radial velocity distribution is indistinguishable from the Orion As population, we suggest that NGC1980 is part of Orion As star formation activity. Based on their stellar parameters and kinematic properties, we identify 383 new candidate members of Orion A, most of which are diskless sources in areas of the region poorly studied by previous works.
This paper continues our study of the foreground population to the Orion molecular clouds. The goal is to characterize the foreground population north of NGC 1981 and to investigate the star formation history in the large Orion star-forming region. W
e focus on a region covering about 25 square degrees, centered on the $epsilon$ Orionis supergiant (HD 37128, B0,Ia) and covering the Orion Belt asterism. We used a combination of optical (SDSS) and near-infrared (2MASS) data, informed by X-ray (textit{XMM-Newton}) and mid-infrared (WISE) data, to construct a suite of color-color and color-magnitude diagrams for all available sources. We then applied a new statistical multiband technique to isolate a previously unknown stellar population in this region. We identify a rich and well-defined stellar population in the surveyed region that has about 2,000 objects that are mostly M stars. We infer the age for this new population to be at least 5, Myr and likely $sim10$,Myr and estimate a total of about 2,500 members, assuming a normal IMF. This new population, which we call the Orion Belt population, is essentially extinction-free, disk-free, and its spatial distribution is roughly centered near $epsilon$ Ori, although substructure is clearly present. The Orion Belt population is likely the low-mass counterpart to the Ori OB Ib subgroup. Although our results do not rule out Blaauws sequential star formation scenario for Orion, we argue that the recently proposed blue streams scenario provides a better framework on which one can explain the Orion star formation region as a whole. We speculate that the Orion Belt population could represent the evolved counterpart of an Orion nebula-like cluster.
We describe the results of a very deep imaging survey of the Trapezium Cluster in the IJH bands, using the UKIRT high resolution camera UFTI. Approximately 32% of the 515 point sources detected are brown dwarf candidates, including several free float
ing objects with masses below the Deuterium burning (planetary) threshold at 0.013 solar masses, which are detectable because of their extreme youth. We have confidence that almost all the sources detected are cluster members, since foreground contamination is minimal in the 33 arcmin^2 area surveyed and the dense backdrop of OMC-1 obscures all background stars at these wavelengths. Extinction is calculated from the (J-H)colours, permitting accurate luminosity estimates and temperatures are derived from the dereddened (I-J) colours. There is some evidence for a cut-off in the luminosity function below the level corresponding to several Jupiter masses, which may represent the bottom end of the IMF. Since star formation is complete in the Trapezium this limit could have wide significance, if confirmed. However, it could well be an effect of the dispersal of the molecular cloud by the central O-type stars, a process whose timescale will vary between star formation regions.
Following the recent discovery of a large population of young stars in front of the Orion Nebula, we carried out an observational campaign with the DECam wide-field camera covering ~10~deg^2 centered on NGC 1980 to confirm, probe the extent of, and c
haracterize this foreground population of pre-main-sequence stars. We confirm the presence of a large foreground population towards the Orion A cloud. This population contains several distinct subgroups, including NGC1980 and NGC1981, and stretches across several degrees in front of the Orion A cloud. By comparing the location of their sequence in various color-magnitude diagrams with other clusters, we found a distance and an age of 380pc and 5~10Myr, in good agreement with previous estimates. Our final sample includes 2123 candidate members and is complete from below the hydrogen-burning limit to about 0.3Msun, where the data start to be limited by saturation. Extrapolating the mass function to the high masses, we estimate a total number of ~2600 members in the surveyed region. We confirm the presence of a rich, contiguous, and essentially coeval population of about 2600 foreground stars in front of the Orion A cloud, loosely clustered around NGC1980, NGC1981, and a new group in the foreground of the OMC-2/3. For the area of the cloud surveyed, this result implies that there are more young stars in the foreground population than young stars inside the cloud. Assuming a normal initial mass function, we estimate that between one to a few supernovae must have exploded in the foreground population in the past few million years, close to the surface of Orion A, which might be responsible, together with stellar winds, for the structure and star formation activity in these clouds. This long-overlooked foreground stellar population is of great significance, calling for a revision of the star formation history in this region of the Galaxy.
Stars form in molecular clouds in the interstellar medium (ISM) with a turbulent kinematic state. Newborn stars therefore should retain the turbulent kinematics of their natal clouds. Gaia DR2 and APOGEE-2 surveys in combination provide three-dimensi
onal (3D) positions and 3D velocities of young stars in the Orion Molecular Cloud Complex. Using the full 6D measurements, we compute the velocity structure functions (VSFs) of the stars in six different groups within the Orion Complex. We find that the motions of stars in all diffuse groups exhibit strong characteristics of turbulence. Their first-order VSFs have a power-law exponent ranging from $sim0.2-0.5$ on scales of a few to a few tens of pc, generally consistent with Larsons relation. On the other hand, dense star clusters, such as the Orion Nebula Cluster (ONC), have experienced rapid dynamical relaxation, and have lost the memory of the initial turbulent kinematics. The VSFs of several individual groups and the whole Complex all show features supporting local energy injection from supernovae. The measured strength of turbulence depends on the location relative to the supernova epicenters and the formation history of the groups. Our detection of turbulence traced by young stars introduces a new method of probing the turbulent kinematics of the ISM. Unlike previous gas-based studies with only projected measurements accessible to observations, we utilize the full 6D information of stars, presenting a more complete picture of the 3D interstellar turbulence.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
