اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدGalactic Cepheids with Spitzer: II. Search for Extended Infrared Emission
172
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A deep and detailed examination of 29 classical Cepheids with the Spitzer Space Telescope has revealed three stars with strong nearby extended emission detected in multiple bands which appears to be physically associated with the stars. RS Pup was already known to possess extended infrared emission, while the extended emission around the other two stars S Mus and delta Cep is newly discovered in our observations. Four other stars GH Lup, l Car, T Mon and X Cyg show tentative evidence for extended infrared emission. An unusual elongated extended object next to SZ Tau appears to be a background or foreground object in a chance alignment with the Cepheid. The inferred mass loss rates upper limits for S Mus and delta Cep are in the range from 1e-9 to 1e-8 Msun/yr, with the upper limit for RS Pup as high as 1e-6 Msun/yr. Mass loss during post-main-sequence evolution has been proposed as a resolution to the discrepancy between pulsational and dynamical masses of Cepheid variable stars: dust in the lost material would make itself known by the presence of an infrared bright nebula, or unresolved infrared excess. The observed frequency of infrared circumstellar emission (<24%) and the mass loss rate we estimate for our sources shows that dusty mass loss can only account for part of the Cepheid mass loss discrepancy. Nevertheless, our direct evidence that mass loss is active during the Cepheid phase is an important confirmation that these processes need to be included in evolutionary and pulsation models of these stars, and should be taken into account in the calibration of the Cepheid distance scale.
قيم البحث
اقرأ أيضاً
We present a new extended and detailed set of models for Classical Cepheid pulsators at solar chemical composition ($Z=0.02$, $Y=0.28$) based on a well tested nonlinear hydrodynamical approach. In order to model the possible dependence on crucial ass
umptions such as the Mass-Luminosity relation of central Helium burning intermediate-mass stars or the efficiency of superadiabatic convection, the model set was computed by varying not only the pulsation mode and the stellar mass but also the Mass-Luminosity relation and the mixing length parameter that is used to close the system of nonlinear hydrodynamical and convective equations. The dependence of the predicted boundaries of the instability strip as well as of both light and radial velocity curves on the assumed Mass-Luminosity and the efficiency of superadiabatic convection is discussed. Nonlinear Period-Mass-Luminosity-Temperature, Period-Radius and Period-Mass-Radius relations are also computed. The theoretical atlas of bolometric light curves for both the fundamental and first overtone mode has been converted in the Gaia filters $G$, $G_{BP}$ and $G_{BR}$ and the corresponding mean magnitudes have been derived. Finally the first theoretical Period-Luminosity-Color and Period-Wesenheit relations in the Gaia filters are provided and the resulting theoretical parallaxes are compared with Gaia Data Release 2 results for both fundamental and first overtone Galactic Cepheids.
In a step toward understanding the origin of the Galactic Halo, we have reexamined Type II Cepheids (T2C) in the field with new input from the second data release (DR2) of Gaia. For 45 T2C with periods from 1 to 20 days, parallaxes, proper motions, a
nd [Fe/H] values are available for 25 stars. Only 5 show [Fe/H] < -1.5, while the remaining stars show thick disk kinematics and [Fe/H] > -0.90. We have compared the T2C stars of the field with their cousins in the globular clusters of the Halo and found that the globular clusters with T2C stars show metallicities and kinematics of a pure Halo population. The globulars may have formed during the overall collapse of the Galaxy while the individual thick disk T2C stars may have been captured from small systems that self-enriched prior to capture. The relationship of these two populations to the micro-galaxies currently recognized as surrounding the Galaxy is unclear.
The infrared data from the Spitzer Space Telescope has provided an invaluable tool for identifying physical processes in star formation. In this study we calculate the IRAC color space of UV fluorescent molecular hydrogen (H$_2$) and Polycyclic Aroma
tic Hydrocarbon (PAH) emission in photodissociation regions (PDRs) using the Cloudy code with PAH opacities from Draine & Li 2007. We create a set of color diagnostics that can be applied to study the structure of PDRs and to distinguish between FUV excited and shock excited H$_2$ emission. To test this method we apply these diagnostics to Spitzer IRAC data of NGC 2316. Our analysis of the structure of the PDR is consistent with previous studies of the region. In addition to UV excited emission, we identify shocked gas that may be part of an outflow originating from the cluster.
The Galactic center (GC) is the densest region of the Milky Way. Variability surveys towards the GC potentially provide the largest number of variable stars per square degree within the Galaxy. However, high stellar density is also a drawback due to
blending. Moreover, the GC is affected by extreme reddening, therefore near infrared observations are needed. We plan to detect new variable stars towards the GC, focusing on type II Cepheids (T2Cs) which have the advantage of being brighter than RR Lyrae stars. We perform parallel Lomb-Scargle and Generalized Lomb-Scargle periodogram analysis of the $K_s$-band time series of the VISTA variables in the Via Lactea survey, to detect periodicities. We employ statistical parameters to clean our sample. We take account of periods, light amplitudes, distances, and proper motions to provide a classification of the candidate variables. We detected 1,019 periodic variable stars, of which 164 are T2Cs, 210 are Miras and 3 are classical Cepheids. We also found the first anomalous Cepheid in this region. We compare their photometric properties with overlapping catalogs and discuss their properties on the color-magnitude and Bailey diagrams. We present the most extensive catalog of T2Cs in the GC region to date. Offsets in E($J-K_s$) and in the reddening law cause very large ($sim$1-2 kpc) uncertainties on distances in this region. We provide a catalog which will be the starting point for future spectroscopic surveys in the innermost regions of the Galaxy.
We discuss 94 Extended Green Objects (EGOs) in the northern Galactic plane cataloged by Cyganowski et al, based on near-infrared narrowband H2 (2.122 {mu}m and continuum observations from the United Kingdom Infrared Telescope. This data set is three
times larger than our previous study, and is unbiased by preselection. As discussed in the previous paper, the morphologies of the 4.5 {mu}m emission generally resemble those of the near-infrared continuum, but are different from those of the H2 emission. Of our sample, only 28% of EGOs with H2 emission show similar morphologies between 4.5 {mu}m and H2 emission. These results suggest that the 4.5 {mu}m emission mainly comes from scattered continuum from the embedded young stellar object (YSO), and partially from H2 emission. About half of EGOs are associated with H2 outflows, if the H2 outflow incompleteness is considered. The H2 outflow detection rate for EGOs with K-band detections (61%) is significantly higher than for those without K-band detections (36%). This difference may be due to the fact that both H2 and K-band emissions are associated with outflows, i.e., H2 emission and K-band continuum are associated with shocks and outflow cavities, respectively. We also compared the correlation between the H2 outflows and Class I 44 GHz methanol masers from literature. The methanol masers can be located upstream or downstream of the H2 outflows and some bright H2 spots or outflows are not associated with methanol masers, suggesting that methanol masers and H2 emission trace different excitation conditions.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
