The results of a combined astrometric, photometric, and spectroscopic program to identify members of the open cluster IC 4665 are presented. Numerous new proper motion/photometric candidate members and at least 23 M dwarfs with H-alpha emission have been identified. A reanalysis of IC 4665's age using different methods yields conflicting results ranging from approx. 3x10^7^ yr to the age of the Pleiades. This study provides a list of candidate cluster members in the intermediate and low-mass regime of this cluster. Future spectroscopic observations of these candidates should eventually identify true cluster members. The results of new echelle observations of some candidates and the photometric monitoring of one apparent cluster member are given in an appendix.
We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identified by the search for associations containing young stars survey. In addition to common kinematics and ages between these two systems, here we explore their chemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogeneous high-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argus association using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba. All stars in the open cluster and Argus association were found to share similar abundances with the scatter well within the uncertainties, where [Fe/H]=-0.04+/-0.03 for cluster stars and [Fe/H]=-0.06+/-0.05 for Argus stars. Effects of overionization/excitation were seen for stars cooler than roughly 5200K as previously noted in the literature. Also, enhanced Ba abundances of around 0.6dex were observed in both systems. The common ages, kinematics and chemical abundances strongly support the fact that the Argus association stars originated from the open cluster IC 2391. Simple modelling of this system finds this dissolution to be consistent with two-body interactions.
Bright-rimmed clouds (BRCs) are formed at the periphery of HII regions as the radiation from the central star interacts with dense gas. The ionization and resulting compression of the clouds may lead to cloud disruption causing secondary star formation depending on the stellar and gas parameters. Here we use R-band polarimetry to probe the plane-of-the sky magnetic field for two nearby BRCs, IC 59 and IC 63. Both nebulae are illuminated by {gamma} Cas with the direction of the ionizing radiation being orientated parallel or perpendicular to the local magnetic field, allowing us to probe the importance of magnetic field pressure in the evolution of BRCs. Because of the proximity of the system (~200pc), we have acquired a substantial sample of over 500 polarization measurements for stars that form the background to the nebulae. On large scales, the magnetic field geometries of both clouds are anchored to the ambient magnetic field. For IC 63, the magnetic field is aligned parallel to the head-tail morphology of the main condensation, with a convex morphology relative to the direction of the ionizing radiation. We estimate the plane-of-the-sky magnetic field strength in IC 63 to be ~90{mu}G. In IC 59, the projected magnetic field follows the M-shape morphology of the cloud. Here, field lines present a concave shape with respect to the direction of the ionizing radiation from {gamma} Cas. Comparing our observations to published theoretical models, we find good general agreement, supporting the importance of magnetic fields in BRC evolution.
JHKs photometry is presented from a 3-yr survey of the central regions of the Local Group dwarf irregular galaxy IC 1613. The morphologies of the colour-magnitude and colour-colour diagrams are discussed with particular reference to the supergiants and M- and C-type asymptotic giant branch (AGB) stars. Mean JHKs magnitudes, amplitudes and periods are given for five O-rich and nine C-rich Mira variables for which bolometric magnitudes are also estimated. A distance of 750kpc ((m-M)0=24.37+/-0.08mag) is derived for IC 1613 by fitting a period-luminosity (PL) relation to the C-rich Miras. This is in agreement with values from the literature. The AGB stars exhibit a range of ages. A comparison with theoretical isochrones suggests that four luminous O-rich Miras are as young as 2x10^8^yr. One of these has a lithium absorption line in its spectrum, demonstrating that it is undergoing hot bottom burning (HBB). This supports the idea that HBB is the cause of the high luminosity of these AGB stars, which puts them above the fundamental PL relation. Further studies of similar stars, selected from their positions in the PL diagram, could provide insight into HBB. A much fainter, presumed O-rich, Mira is similar to those found in Galactic globular clusters. The C Miras are of intermediate age. The O-rich variables are not all recognized as O-rich, or even as AGB stars, on the basis of their J-Ks colour. It is important to appreciate this when using near-infrared surveys to classify AGB stars in more distant galaxies.
Rich, young stellar clusters produce H II regions whose expansion into the nearby molecular cloud is thought to trigger the formation of new stars. However, the importance of this mode of star formation is uncertain. This investigation seeks to quantify triggered star formation (TSF) in IC 1396A (aka the Elephant Trunk Nebula), a bright-rimmed cloud (BRC) on the periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37 cluster. X-ray selection of young stars from Chandra X-ray Observatory data is combined with existing optical and infrared surveys to give a more complete census of the TSF population. Over 250 young stars in and around IC 1396A are identified; this doubles the previously known population. A spatio-temporal gradient of stars from the IC 1396A cloud towards the primary ionizing star HD 206267 is found. The current project consists of two Chandra-ACIS X-ray observations of IC 1396A, a Guaranteed Time observation (ObsID No. 11807 obtained on 2010 March 31; PI: Garmire) and a Guest Observer observation (ObsID No. 10990 obtained on 2010 June 9; PI: Getman). Both observations were pointed at the head of the globule but had different roll angles. For each observation, the authors considered only results arising from the imaging array (ACIS-I) of four abutted 1024 x 1024 pixel front-side illuminated charge-coupled devices (CCDs) covering about 17 x 17 arcmin<sup>2</sup> on the sky, Similar to the Chandra catalog of X-ray sources in the Carina Nebula (Broos et al. 2011, ApJS, 194, 2), this list of candidate sources in IC 1396A is trimmed to omit sources with fewer than 3 total source counts (the sum of the net counts and the background counts, NC + BC < 3) and the probability for being a background fluctuation greater than 1% (prob_no_src > 0.01). The final catalog comprises 415 X-ray sources, roughly half of which sources are extragalactic with extremely optically faint counterparts (Section 3.2 of the reference paper), and the rest are young stars associated with the Trumpler 37 and IC 1396A star-forming regions. UVR<sub>c</sub> I<sub>c</sub> observations were carried out with the 1.2-m telescope at the Fred Lawrence Whipple Observatory (FLWO), using the 4Shooter CCD array, between 2000 September and 2002 September. 4Shooter is an array of four CCDs, covering a square of 25 arcminutes on the side. Two 4Shooter fields were taken to cover an ~45 x 25 arcmin<sup>2</sup> area centered on the star HD 206267. The FLWO fields contain the whole ACIS field, except for a small gap in between the four CCDs of 4Shooter. All but a few Chandra stars were observed in 2000 September. UVR<sub>J</sub> I<sub>J</sub> observations of Trumpler 37/IC 1396A were obtained in service mode during three nights in 2007 June 9-11 using the wide-field camera, LAICA, mounted on the 3.5-m telescope in Calar Alto, Spain. LAICA is a 2 x 2 mosaic of four CCDs, each covering a 15.3 x 15.3 arcmin<sup>2</sup> field of view (FOV) with a large gap of 15.3 x 15.3 arcmin<sup>2</sup> in between. The project combines four LAICA pointings covering an ~45 x 45 arcmin<sup>2</sup> area around HD 206267, including nearly the entire ACIS field. The Spitzer observation was obtained on 2003 December 20 with the IRAC detector in all four IRAC channels (3.6, 4.5, 5.8 and 8.0 micron). Two adjacent fields subtending ~37 x 42 arcmin<sup>2</sup> in channel pairs 3.6/5.8 micron and 4.5/8.0 micron were centered on Trumpler 37. To reduce unnecessary data processing the authors analyzed only a portion of the original data that encompassed the Chandra-ACIS field with a coverage of ~19 x 19 arcmin<sup>2</sup> area in all four channels centered on Rim A of the IC 1396A globule. This covers 93% of the ACIS field omitting its north-western and south-western edges. An automated cross-correlation between the Chandra source positions and the optical-IR source positions was made using a search radius of 2 arcseconds within ~6 arcminutes of the ACIS field center, and a search radius of 3.5 arcseconds in the outer regions of the ACIS field where the X-ray source positions are more uncertain due to the deterioration of the Chandra telescope PSF. This was followed by a careful visual examination of each source in both bands to remove dubious sources and associations. This table was created by the HEASARC in April 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/426/2917">CDS Catalog J/MNRAS/426/2917</a> files table1.dat, table2.dat, and table3.dat. This is a service provided by NASA HEASARC .
The results of a UBV CCD photometric study of the cluster IC 4996 are presented. We obtain new values for the cluster parameters: E(B-V)=0.71+/-0.08, V_0_-M_V_=11.9+/-0.1, and age=(7.5+/-3)x10^6^yr. The combined evidence from the photometric diagrams suggests the presence of a number of premain-sequence (PMS) cluster members with spectral types ~A0 to F5. The interpretation of these objects as PMS candidates is further supported by independent results from CCD uvbyH{beta} observations. If confirmed, these stars would bridge the existing gap in the sample of PMS stars, between the coolest Herbig AeBe stars (HAeBe), and the hottest T Tauri stars. These PMS candidates are located some 0.5 and 1 mag above the main sequence in the V-(B-V) diagram, around the location of spectral types AF. This feature, together with their locations in the (U-B)-(B-V) diagram and the interpretation that they are PMS members, suggest an additional reddening law with a slope {alpha}=E(U-B)/E(B-V)~0.55, probably caused by circumstellar material.
One-thousand one-hundred ninety-seven observations of 730 binary star systems, observed by means of speckle interferometry with the 4m telescope on Kitt Peak, are presented. Included in these binary stars are new interferometric companions to five visual binaries. These measurements, made mostly during the period 1991 to 1993, comprise the 11th installment of results stemming from our speckle program at the 4m class telescopes on Kitt Peak, Cerro Tololo, and Mauna Kea.
We present 2017 observations of 1286 binary stars, observed by means of speckle interferometry using six telescopes over a 15 year period from 1982 April to 1997 June. These measurements constitute the 23d installment in CHARA's speckle program at 2 to 4 m class telescopes and include the second major collection of measurements from the Mount Wilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are also presented for 14 systems, seven of which have had no previously published orbital analyses.
IC 348 is a nearby (~ 310 pc), young (~ 2 - 3 Myr) open cluster with > 300 members identified from optical and infrared observations. The authors studied the properties of the coronae of the young low-mass stars in IC 348, combining X-ray and optical/infrared data. The four existing Chandra observations of IC 348 were merged, thus providing a deeper and spatially more complete X-ray view than previous X-ray studies of the cluster. The authors compiled a comprehensive catalog of IC 348 members taking into account recent updates to the cluster census. Their data collection comprises fundamental stellar parameters, infrared excess indicating the presence of disks, H-alpha emission as a tracer of chromospheric emission or accretion, and mass accretion rates. The authors have detected 290 X-ray sources in four merged Chandra exposures, of which 185 are associated with known cluster members corresponding to a detection rate of ~ 60% for the cluster members of IC 348 identified in optical/infrared studies. According to the most recent spectral classification of IC 348 members, only four of the X-ray sources are brown dwarfs (spectral type M6 and later). The detection rate is highest for diskless Class III stars and increases with stellar mass. This may be explained with higher X-ray luminosities for higher mass and later evolutionary stage that is evident in the X-ray luminosity functions. In particular, the authors find that for the lowest examined masses (0.1 M<sub>sun</sub> - 0.25 M<sub>sun</sub>) there is a difference between the X-ray luminosity functions of accreting and non-accreting stars (classified on the basis of their H-alpha emission strength) as well as those of disk-bearing and diskless stars (classified on the basis of the slope of the spectral energy distribution). These differences disappear for higher masses. This is related to the finding that the L<sub>x</sub>/L<sub>bol</sub> ratio is non-constant across the mass/luminosity sequence of IC 348 with a decrease towards lower luminosity stars. Their analysis of an analogous stellar sample in the Orion Nebula Cluster suggests to the authors that the decline of L<sub>x</sub>/L<sub>bol</sub> for young stars at the low-mass end of the stellar sequence is likely universal. X-ray fluxes are presented for all (185) known optical/infrared IC348 members which were observed and detected by Chandra. The basic source parameters for all X-ray sources, i.e., including an additional 105 sources not associated with known IC 348 members, are given. The X-ray flux upper limits for 129 IC 348 members which were observed but not detected by Chandra (present in the as published version of Table 3 from the reference paper) are not included in this HEASARC representation of the data given in Tables 3 and 7 from the reference paper. Thus, this table contains 290 (185 + 105) rows, one for each X-ray source (IC 348 member or not) detected by Chandra in the direction of IC 348. This HEASARC table was created in February 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/537/A135">CDS Catalog J/A+A/537/A135</a> files table3.dat and table7.dat. It lists the X-ray counts and other properties for the 290 Chandra X-ray sources which were listed in table7.dat. It does not include the X-ray flux upper limits for 129 non-detected IC 348 members which were given in table3.dat, so only the X-ray fluxes and luminosities for the 185 X-ray detected IC 348 members given in table3.dat are included in this table. Notice that in the CDS version there were 2 duplicate entries in table3.dat. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018. This is a service provided by NASA HEASARC .
The authors monitored the Cassiopeia dwarf galaxy (IC 10) in a series of 10 Chandra ACIS-S observations to capture its variable and transient X-ray source population, which is expected to be dominated by High Mass X-ray Binaries (HMXBs). They present a sample of 21 X-ray sources that are variable between observations at the 3-sigma level, from a catalog of 110 unique point sources (the HEASARC notes that there are actually 111 sources in the CDS version of the catalog from which this HEASARC table originates). The authors find four transients (flux variability ratio greater than 10) and a further eight objects with ratios >5. The observations span the years 2003-2010 and reach a limiting luminosity of >10<sup>35</sup> erg/s, providing sensitivity to X-ray binaries in IC 10 as well as flare stars in the foreground Milky Way. The nature of the variable sources is investigated from light curves, X-ray spectra, energy quantiles, and optical counterparts. The purpose of this study is to discover the composition of the X-ray binary population in a young starburst environment. IC 10 provides a sharp contrast in stellar population age (<10 million years) when compared to the Magellanic Clouds (40-200 Myr) where most of the known HMXBs reside. The authors find 10 strong HMXB candidates, 2 probable background active galactic nuclei, 4 foreground flare-stars or active binaries, and 5 not yet classifiable sources. Complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper X-ray observations to obtain higher S/N spectra and search for pulsations. A catalog (contained in this HEASARC table) has been created and supporting data sets (the data used to create the light curves shown in Figures 3, 4 and 5 in the reference paper) are available at <a href="http://cdsarc.u-strasbg.fr/ftp/cats/J/ApJ/836/50/">http://cdsarc.u-strasbg.fr/ftp/cats/J/ApJ/836/50/</a>. A monitoring series of 7x15 ks Chandra/ACIS observations, spaced at roughly six-week intervals was obtained during 2009-2010. A pair of very deep ACIS-S3 observations (2x45ks) made in 2006 November provided a reference data set for improved source positions and spectral information. The original Wang+ (2005, MNRAS, 362, 1065) Chandra (ACIS-S3) observation of 30 ks made in 2003 was also included in this analysis. The complete listing of 10 Chandra observation identifiers (ObsIDs) comprising the data set is summarized in Table 1 of the reference paper, also shown here: <pre> MJD |Date |ObsID|Flag|Exp.|RA(J2000)Dec(J2000)|Roll|Num. Sources ks hh mm ss dd mm ss deg. 52710.7|2003 Mar 12 |03953|a |28.9|00 20 25 +59 16 55|339.27|31 54041.8|2006 Nov 2 |07082| |40.1|00 20 04 +59 16 45|223.70|48 54044.2|2006 Nov 5 |08458| |40.5|00 20 04 +59 16 45|223.70|41 55140.7|2009 Nov 5 |11080| |14.6|00 20 17 +59 17 56|226.53|19 55190.2|2009 Dec 25 |11081| | 8.1|00 20 19 +59 18 02|286.15|24 55238.5|2010 Feb 11 |11082| |14.7|00 20 23 +59 17 10|320.56|24 55290.6|2010 Apr 4 |11083| |14.7|00 20 34 +59 19 01| 10.32|25 55337.8|2010 May 21 |11084| |14.2|00 20 25 +59 20 16| 67.89|27 55397.5|2010 Jul 20 |11085| |14.5|00 20 11 +59 19 13|121.25|22 55444.6|2010 Sep 5 |11086| |14.7|00 20 15 +59 18 11|157.71|27 |2006 Nov 2-5 |57082|b |80.6|00 20 04 +59 16 45|223.70|63 </pre> Flag values as follows: <pre> a = ObsID 03953 used about half of the CCD area in subarray mode. b = Merged 2006 data set referred to as ObsID 57082 consists of the nearly contiguous ObsIDs 07082 and 08458, which had identical pointings. </pre> Roll is the spacecraft roll angle, and Num. Sources is the number of unique point sources detected in each observation after combining wavdetect lists from the soft (S: 0.3-1.5 keV), broad (B: 0.3-8 keV) and hard (H: 2.5-8 keV) energy bands. This table was created by the HEASARC in November 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/836/50">CDS Catalog J/ApJ/836/50</a> file table2.dat. This is a service provided by NASA HEASARC .