A near-infrared variability study in the cloud IC1396W: low star-forming efficiency and two new eclipsing binaries (original) (raw)
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Near-Infrared Variability Among Young Stellar Objects in the Star Formation Region Cygnus OB7
The Astrophysical Journal, 2013
We present an analysis of near-infrared time-series photometry in J, H, and K bands for about 100 epochs of a 1 • × 1 • region of the Lynds 1003/1004 dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field Infrared Survey Explorer (WISE), we identify 96 candidate disk bearing young stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or earlier. Using the Wide-Field imaging CAMera (WFCAM) on the United Kingdom InfraRed Telescope (UKIRT), we were able to obtain photometry over three observing seasons, with photometric uncertainty better than 0.05 mag down to J ≈ 17. We study detailed light curves and color trajectories of ∼50 of the YSOs in the monitored field. We investigate the variability and periodicity of the YSOs and find the data are consistent with all YSOs being variable in these wavelengths on time scales of a few years. We divide the variability into four observational classes: 1) stars with periodic variability stable over long timescales, 2) variables which exhibit short-lived cyclic behavior, 3) long duration variables, and 4) stochastic variables. Some YSO variability defies simple classification. We can explain much of the observed variability as being due to dynamic and rotational changes in the disk, including an asymmetric or changing blocking fraction, changes to the inner disk hole size, as well as changes to the accretion rate. Overall, we find that the Class I:Class II ratio of the cluster is consistent with an age of < 1 Myr, with at least one individual, wildly varying, source ∼ 100, 000 yr old. We have also discovered a Class II eclipsing binary system with a period of 17.87 days.
STAR FORMATION ACTIVITY IN THE LONG, FILAMENTARY INFRARED DARK CLOUD G53.2
The Astrophysical Journal, 2015
We present star formation activity in the infrared dark cloud (IRDC) G53.2, a remarkable IRDC located at Galactic coordinates (l, b) ∼ (53 • .2, 0 • .0) based on the census of young stellar object (YSO) candidates. IRDC G53.2 was previously identified as several IRDCs in mid-IR images, but it is in fact a long ( 45 pc) cloud, well consistent with a CO cloud at v ∼ 23 km s −1 (or at d ∼1.7 kpc). We present a point-source catalog of IRDC G53.2 that contains ∼370 sources from our photometry of the Spitzer MIPS 24 µm data and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Catalog. The classification of the identified sources based on their spectral index and control field analysis to remove field star contamination reveals that IRDC G53.2 is an active star-forming region with ∼300 YSO candidates. We compare the YSO classification based on spectral index, mid-IR colors, and the wavelength range used, which results in consistent classification, except for flat-spectrum objects, with some ambiguity between Class I and II. Comparison of the YSO population in IRDC G53.2 with those of other nearby star-forming clusters indicates that they are similar in age; on the other hand, stronger association with mid-IR stellar sources in IRDC G53.2 compared with other IRDCs indicates that IRDC G53.2 is at a later evolutionary stage among IRDCs. Spatial distribution of the YSO candidates in IRDC G53.2 shows a good correlation with 13 CO column density and far-IR emission, and earlier-class objects tend to be more clustered in the regions with higher density.
The Early Stages of Star Formation in Infrared Dark Clouds: Characterizing the Core Dust Properties
The Astrophysical Journal, 2010
Identified as extinction features against the bright Galactic mid-infrared background, infrared dark clouds (IRDCs) are thought to harbor the very earliest stages of star and cluster formation. In order to better characterize the properties of their embedded cores, we have obtained new 24 µm, 60-100 µm, and submillimeter continuum data toward a sample of 38 IRDCs. The 24 µm Spitzer images reveal that while the IRDCs remain dark, many of the cores are associated with bright 24 µm emission sources, which suggests that they contain one or more embedded protostars. Combining the 24 µm, 60-100 µm, and submillimeter continuum data, we have constructed broadband spectral energy distributions (SEDs) for 157 of the cores within these IRDCs and, using simple gray-body fits to the SEDs, have estimated their dust temperatures, emissivities, opacities, bolometric luminosities, masses and densities. Based on their Spitzer/IRAC 3-8 µm colors and the presence of 24 µm point source emission, we have separated cores that harbor active, high-mass star formation from cores that are quiescent. The active 'protostellar' cores typically have warmer dust -2temperatures and higher bolometric luminosities than the more quiescent, perhaps 'pre-protostellar', cores. Because the mass distributions of the populations are similar, however, we speculate that the active and quiescent cores may represent different evolutionary stages of the same underlying population of cores. Although we cannot rule out low-mass star-formation in the quiescent cores, the most massive of them are excellent candidates for the 'high-mass starless core' phase, the very earliest in the formation of a high-mass star.
STAR FORMATION IN THE MASSIVE “STARLESS” INFRARED DARK CLOUD G0.253+0.016
The Astrophysical Journal, 2013
G0.253+0.016 is a remarkable massive infrared dark cloud located within ∼100 pc of the galactic center. With a high mass of 1.3 × 10 5 M ⊙ , a compact average radius of ∼2.8 pc and a low dust temperature of 23 K, it has been believed to be a yet starless precursor to a massive Arches-like stellar cluster. We present sensitive JVLA 1.3 and 5.6 cm radio continuum observations that reveal the presence on three compact thermal radio sources projected against this cloud. These radio sources are interpreted as HII regions powered by ∼B0.5 ZAMS stars. We conclude that although G0.253+0.016 does not show evidence of O-type star formation, there are certainly early B-type stars embedded in it. We detect three more sources in the periphery of G0.253+0.016 with non-thermal spectral indices. We suggest that these sources may be related to the galactic center region and deserve further study.
Star formation in the southern dark cloud DC 287.1+02.4
Astronomy & Astrophysics, 2006
Aims. We report the discovery of a group of 12 new infrared sources seen toward IRAS 10501-5630 and the southern dark globule DC 287.1+02.4. The globule appears as a round patch of extinction in optical images with a typical diameter of 5 arcmin. Methods. The sources are seen on Ks and L band images taken using SOFI at the NTT and ISAAC at the VLT. The globule was mapped in millimeter molecular transitions (CO(1-0), C 18 O(1-0), C 18 O(2-1), CS(2-1), HCN(1-0)) using the SEST telescope. Results. Millimeter-wave spectroscopy revealed a single dense core seen in C 18 O, CS, and HCN, extending about 2 arcmin. The infrared sources are likely to be embedded in the dense cloud core. The reddest of the new infrared sources, named here DC 287.1+02.4 IRS, is not detected shortward of 2 µm, and it exhibits a very red (Ks − L) colour. The location and colour of this source suggest that this is the near-infrared counterpart of IRAS 10501-5630. Red nebular emission with an elongated shape is also seen in the H and Ks band images and could be due to scattered light originating in the embedded objects.
Star Formation in the Southern Dark Cloud DC 296.2-3.6
The Astronomical Journal, 2008
We report near-and mid-infrared (IR) images of the southern hemisphere dark cloud DC 296.2−3.6 associated with IRAS 11431−6516. The K s and L images show the presence of an IR nebulosity at the center of the dark cloud (DC). From the analysis of the near-IR color-color diagrams we have identified a young stellar population in the region. Five of these young stellar objects, here named A, B, C, D, and E, were also detected in the mid-IR. Sources B, D, and E are Class I-II T Tauri as suggested by the analysis of their spectral energy distributions. In addition, source E shows a long-term near-IR variability. The near-IR colorcolor diagrams indicate the presence of circumstellar dust envelope in sources A, B, D, and E, while the fit of SEDs of the intermediate-and low-mass objects A and B with a radiation transfer model including infalling envelope+disk+central source suggests circumstellar disks around these two objects. These results indicate that DC 296.2−3.6, located in the far Carina arm, is associated with an embedded cluster of low-mass young stellar objects.
Astronomy and Astrophysics, 2010
Context. The emission nebula N66 is the brightest H II region in the Small Magellanic Cloud (SMC), the stellar association NGC 346 being located at its center. The youthfulness of the region NGC 346/N66 is well documented by studies of the gas and dust emission, and the detection in the optical of a rich sample of pre-main sequence (PMS) stars, and in the mid-and far-IR of young stellar objects (YSOs). However, a comprehensive study of this region has not been performed in the near-IR that would bridge the gap between previous surveys. Aims. We perform a photometric analysis on deep, seeing-limited near-IR VLT images of the region NGC 346/N66 and a nearby control field of the SMC to locate the centers of active high-and intermediate-mass star formation by identifying near-IR bright objects as candidate stellar sources under formation. Methods. We use archival imaging data obtained with the high-resolution camera ISAAC at VLT of NGC 346/N66 to construct the near-IR color-magnitude (CMD) and color-color diagrams (C-CD) of all detected sources. We investigate the nature of all stellar populations in the observed CMDs, and we identify all stellar sources that show significant near-IR excess emission in the observed C-CD. We, thus, select the most likely young stellar sources.
The stellar population and complex structure of the bright-rimmed cloud IC 1396N
Astronomy & Astrophysics, 2009
Context. IC 1396N is a bright-rimmed cloud associated with an intermediate-mass star-forming region, where a number of Herbig-Haro objects, H2 jet-like features, CO molecular outflows, and millimeter compact sources have been observed. Aims. To study in detail the complex structure of the IC 1396N core and the molecular outflows detected in the region and to reveal the presence of additional YSOs inside this globule. Methods. We carried out a deep survey of the IC 1396N region in the J, H, K' broadband filters and deep high-angular resolution observations in the H2 narrowband filter with NICS at the TNG telescope. The completeness limits in the 2MASS standard are Ks~17.5, H~18.5 and J~19.5. Results. A total of 736 sources have been detected in all three bands within the area where the JHK' images overlap. There are 128 sources detected only in HK', 67 detected only in K', and 79 detected only in H. We found only few objects exhibiting a Near-Infrared excess and no clear signs of clustering of sources towards the southern rim. In case of triggered star formation in the southern rim of the globule, this could be very recent, because it is not evidenced through Near-Infrared imaging alone. The H2 emission is complex and knotty and shows a large number of molecular hydrogen features spread over the region, testifying a recent star-formation activity throughout the whole globule. This emission is resolved into several chains or groups of knots that sometimes show a jet-like morphology. The shocked cloudlet model scenario previously proposed to explain the V-shaped morphology of the CO molecular outflow powered by the intermediate-mass YSO BIMA 2 seems to be confirmed by the presence of H2 emission at the position of the deflecting western clump. New possible flows have been discovered in the globule,
Astronomy & Astrophysics
Context. Star formation in the outer Galaxy, namely, outside of the Solar circle, has not been extensively studied in part due to the low CO brightness of the molecular clouds linked with the negative metallicity gradient. Recent infrared surveys provide an overview of dust emission in large sections of the Galaxy, but they suffer from cloud confusion and poor spatial resolution at far-infrared wavelengths. Aims. We aim to develop a methodology to identify and classify young stellar objects (YSOs) in star-forming regions in the outer Galaxy and use it to resolve a long-standing disparity in terms of the distance and evolutionary status of IRAS 22147+5948. Methods. We used a support vector machine learning algorithm to complement standard color-color and color-magnitude diagrams in our search for YSOs in the IRAS 22147 region, based on publicly available data from the Spitzer Mapping of the Outer Galaxy survey. The agglomerative hierarchical clustering algorithm was used to identify clusters. Then the physical properties of individual YSOs were calculated. The distances were determined using CO 1-0 from the Five College Radio Astronomy Observatory survey. Results. We identified 13 Class I and 13 Class II YSO candidates using the color-color diagrams, along with an additional 2 and 21 sources, respectively, using the applied machine learning techniques. The spectral energy distributions of 23 sources were modeled with a star and a passive disk, corresponding to Class II objects. The models of three sources include envelopes that are typical for Class I objects. The objects were grouped into two clusters located at a distance of ∼ 2.2 kpc and 5 clusters at ∼ 5.6 kpc. The spatial extent of CO, radio continuum, and dust emission confirms the origin of YSOs in two distinct star-forming regions along a similar line of sight. Conclusions. The outer Galaxy may serve as a unique laboratory for exploring star formation across environments, on the condition that complementary methods and ancillary data are used to properly account for cloud confusion and distance uncertainties.