A Study of Cyg OB2: Pointing the Way Towards Finding Our Galaxy's Super Star Clusters

New optical MK classification spectra have been obtained for 14 OB star candidates identified by Comeron et al. (2002) and presumed to be possible members of the Cyg OB2 cluster. All 14 candidate OB stars observed are indeed early-type stars, strongly suggesting the remaining 31 candidates identified by Comeron et al. are also early-type stars. However, as many as half of the new stars appear to be significantly older than the previously studied optical cluster, making their membership in Cyg OB2 suspect. Despite this, the recognition of Cyg OB2 being a more massive and extensive star cluster than previously realized, along with the recently recognized candidate super star cluster Westerlund 1 only a few kpc away (Clark & Negueruela 2002), reminds us that we are woefully under-informed about the massive cluster population in our Galaxy. Extrapolations of the locally derived cluster luminosity function indicate 10s to perhaps 100 of these very massive open clusters (Mcl ~ 10^4 M_sun, Mv ~ -11) should exist within our galaxy. Radio surveys will not detect these massive clusters if they are more than a few million years old. Our best hope for remedying this shortfall is through deep infrared searches and follow up near-infrared spectroscopic observations, as was used by Comeron et al. to locate candidate members of the Cyg OB2 association.Comment: 30 pages, 12 figures, ApJ in pres

A Radial Velocity Survey of the Cygnus OB2 Association

We conducted a radial velocity survey of the Cygnus OB2 Association over a 6 year (1999 - 2005) time interval to search for massive close binaries. During this time we obtained 1139 spectra on 146 OB stars to measure mean systemic radial velocities and radial velocity variations. We spectroscopically identify 73 new OB stars for the first time, the majority of which are likely to be Association members. Spectroscopic evidence is also presented for a B3Iae classification and temperature class variation (B3 - B8) on the order of 1 year for Cygnus OB2 No. 12. Calculations of the intial mass function with the current spectroscopic sample yield Gamma = -2.2 +/- 0.1. Of the 120 stars with the most reliable data, 36 are probable and 9 are possible single-lined spectroscopic binaries. We also identify 3 new and 8 candidate double-lined spectroscopic binaries. These data imply a lower limit on the massive binary fraction of 30% - 42%. The calculated velocity dispersion for Cygnus OB2 is 2.44 +/- km/s, which is typical of open clusters. No runaway OB stars were found.Comment: 56 pages, 23 figures, 5 tables, accepted for publication in the Astrophysical Journa

Quantitative analysis of WC stars: Constraints on neon abundances from ISO/SWS spectroscopy

Neon abundances are derived in four Galactic WC stars -- gamma Vel (WR11, WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8), and WR146 (WC5+O8) - using mid-infrared fine structure lines obtained with ISO/SWS. Stellar parameters for each star are derived using a non-LTE model atmospheric code (Hillier & Miller 1998) together with ultraviolet (IUE), optical (INT, AAT) and infrared (UKIRT, ISO) spectroscopy. In the case of gamma Vel, we adopt results from De Marco et al. (2000), who followed an identical approach. ISO/SWS datasets reveal the [NeIII] 15.5um line in each of our targets, while [NeII] 12.8um, [SIV] 10.5um and [SIII] 18.7um are observed solely in gamma Vel. Using a method updated from Barlow et al. (1988) to account for clumped winds, we derive Ne/He=3-4x10^-3 by number, plus S/He=6x10^-5 for gamma Vel. Neon is highly enriched, such that Ne/S in gamma Vel is eight times higher than cosmic values. However, observed Ne/He ratios are a factor of two times lower than predictions of current evolutionary models of massive stars. An imprecise mass-loss and distance were responsible for the much greater discrepancy in neon content identified by Barlow et al. Our sample of WC5--8 stars span a narrow range in T* (=55--71kK), with no trend towards higher temperature at earlier spectral type, supporting earlier results for a larger sample by Koesterke & Hamann (1995). Stellar luminosities range from 100,000 to 500,000 Lo, while 10^-5.1 < Mdot/(Mo/yr) < 10^-4.5, adopting clumped winds, in which volume filling factors are 10%. In all cases, wind performance numbers are less than 10, significantly lower than recent estimates. Carbon abundances span 0.08 < C/He < 0.25 by number, while oxygen abundances remain poorly constrained.Comment: 16 pages,7 figures accepted for MNRA

A multi-wavelength census of stellar contents in the young cluster NGC 1624

We present a comprehensive multi-wavelength analysis of the young cluster NGC 1624 associated with the H II region Sh2-212 using optical UBVRI photometry, optical spectroscopy and GMRT radio continuum mapping along with the near-infrared (NIR) JHK archival data. Reddening E(B-V) and distance to the cluster are estimated to be 0.76 - 1.00 mag and 6.0 +/- 0.8 kpc, respectively. Present analysis yields a spectral class of O6.5V for the main ionizing source of the region. The distribution of YSOs in (J-H)/ (H-K) NIR colour-colour diagram shows that a majority of them have A_V $\le$ 4 mag. Based on the NIR excess characteristics, we identified 120 probable candidate YSOs in this region which yield a disk frequency of ~ 20%. These YSOs are found to have an age spread of ~ 5 Myr with a median age of ~ 2-3 Myr and a mass range of ~ 0.1 - 3.0 $M_\odot$. A significant number of YSOs are located close to the cluster centre and we detect an enhanced density of reddened YSOs located/projected close to the molecular clumps at the periphery of NGC 1624. This indicates that the YSOs located within the cluster core are relatively older in comparison to those located/projected near the clumps. From the radio continuum flux, spectral class of the ionizing source of the ultra-compact H II region at the periphery of Sh2-212 is estimated to be ~ B0.5V. From optical data, slope of the mass function (MF) $\Gamma$, in the mass range $1.2 \le M/M_{\odot}<27$ can be represented by a single power law with a slope -1.18 +/- 0.10, whereas the NIR data in the mass range $0.65 \le M/M_{\odot}<27$ yields $\Gamma$ = -1.31 +/- 0.15. The slope of the K-band luminosity function (KLF) for the cluster is found to be 0.30 +/- 0.06 which is in agreement with the values obtained for other young clusters.Comment: Accepted for publication in MNRA

On the nature of the galactic early-B hypergiants

Despite their importance to a number of astrophysical fields, the lifecycles of very massive stars are still poorly defined. In order to address this shortcoming, we present a detailed quantitative study of the physical properties of four early-B hypergiants (BHGs); Cyg OB2 #12, zeta Sco, HD190603 and BP Cru. These are combined with an analysis of their long-term spectroscopic and photometric behaviour in order to determine their evolutionary status. The long-term datasets revealed that they are remarkably stable over long periods (>40yr), with the possible exception of zeta Sco prior to the 20th century, in contrast to the typical excursions that characterise luminous blue variables (LBVs). Zeta Sco, HD190603 and BP Cru possess physical properties intermediate between B supergiants and LBVs; we therefore suggest that BHGs are the immediate descendants and progenitors (respectively) of such stars (for initial masses in the range ~30-60Msun). In contrast, while the wind properties of Cyg OB2 #12 are consistent with this hypothesis, the combination of extreme luminosity and spectroscopic mass (~110Msun) and comparatively low temperature means it cannot be accommodated in such a scheme. Likewise, despite its co-location with several LBVs above the Humphreys-Davidson (HD) limit, the lack of long term variability and its unevolved chemistry apparently excludes such an identification. Since such massive stars are not expected to evolve to such cool temperatures, the properties of Cyg OB2 #12 are difficult to understand under current evolutionary paradigms. [ABRIDGED]Comment: 36 pages, 19 figures (of which 17 pages are online supplemental material). Accepted for publication in Astronomy and Astrophysic

Gene Expression Pattern Analysis of Anterior Hox Genes during Zebrafish (Danio rerio) Embryonic Development Reveals Divergent Expression Patterns from Other Teleosts

The regional identity of organs and organ systems along the anterior-posterior axis during embryonic development is patterned, in part, by Hox genes, which encode transcription factor proteins that activate or repress the expression of downstream target genes. Divergent nested Hox gene expression patterns may have had a role in facilitating morphological divergence of structures, such as the pharyngeal jaw apparatus, among evolutionarily divergent teleost fishes. Recent studies from several evolutionarily divergent teleosts, such as the Japanese Medaka (Oryzias latipes) and the Nile Tilapia (Oreochromis niloticus), have shown the presence of divergent expression patterns of several Hox genes within paralog groups 2–5 between these species. Specifically, these expression patterns were documented in the pharyngeal arches, which give rise to the pharyngeal jaw apparatus. While the expression patterns of several Zebrafish (Danio rerio) Hox genes that are orthologous to those of Medaka and Tilapia have been documented within the developing hindbrain and pharyngeal arches, many still have yet to be documented, especially within the pharyngeal arches during the postmigratory cranial neural crest cell stages. Here, we present the expression patterns of six Zebrafish Hox genes, hoxc3a, d3a, a4a, d4a, b5a, and c5a, within the pharyngeal arches during a postmigratory cranial neural crest cell stage and compare them to their orthologous genes of Medaka and Tilapia at similar stages. We show that while hoxc3a, d3a, and c5a of Zebrafish are absent from the pharyngeal arches, hoxa4a, d4a, and b5a show divergent expression patterns from their orthologs in Medaka and Tilapia. These observed divergences may be, in part, responsible for the divergent pharyngeal jaw apparatus structures exhibited by these fishes

Spectroscopic distances of 28 nearby star candidates

28 hitherto neglected candidates for the Catalogue of Nearby Stars (CNS) were investigated to verify their classification and to improve their distance estimates. All targets had at least a preliminary status of being nearby dwarf stars based on their large proper motions and relatively faint magnitudes. Better photometric and/or spectroscopic distances were required for selecting stars which are worth the effort of trigonometric parallax measurements. Low-resolution spectra were obtained with NASPEC at the Tautenburg 2m telescope and with CAFOS at the Calar Alto 2.2m telescope. The spectral types of M-type stars were determined by direct comparison of the target's spectra with those of comparison stars of known spectral types observed with the same instrument. The classification of earlier types was done based on comparison with published spectral libraries. The majority were classified as M dwarfs including 11 stars within 25 pc. The fainter component of LDS 1365, previously thought to form a nearby common proper motion pair, is according to our results an unrelated high-velocity background star. For several other nearby common proper motion pairs our distance estimates of the fainter components are in good agreement with Hipparcos distances of the brighter components. (abridged)Comment: 5 pages, 4 figures, accepted by Astron. Astrophy

Uptake, Translocation, and Accumulation of Pharmaceutical and Hormone Contaminants in Vegetables

A team led by Wei Zheng, senior research scientist at ISTC, investigated whether our food is at risk of accumulating PPCPs when irrigated with wastewater from concentrated animal feedlot operations (CAFOs) and wastewater treatment plants (WWTPs). The results appeared in Zheng, Wei et al (2014). "Uptake, Translocation, and Accumulation of Pharmaceutical and Hormone Contaminants in Vegetables." in Kyung Myung, Norbert M. Satchivi, and Colleen K. Kingston, eds. Retention, Uptake, and Translocation of Agrochemicals in Plants. Washington, DC : American Chemical Society, 167-181. DOI: 10.1021/bk-2014-1171.ch009.Ope

The nearest cool white dwarf (d~4pc), the coolest M-type subdwarf (sdM9.5), and other high proper motion discoveries

We report the discovery of seven high proper motion stars with proper motions between about 0.7 and 2.2 arcsec/yr. They were detected in an archival search using multi-epoch positions in the optical SuperCOSMOS Sky Surveys and in the near-infrared sky surveys 2MASS and DENIS. The star with the largest proper motion, is spectroscopically classified as a very nearby (d=8pc) M5.5 dwarf with Galactic thin disk kinematics. A second star with about 2 arcsec/yr proper motion, is still lacking spectroscopic confirmation but can be classified from photometry as thick disk M3.5 dwarf. Three objects turn out to be cool subdwarf members of the Galactic thick disk or halo, including the first sdM9.5 object, which represents the currently coolest known M subdwarf, another ultra-cool subdwarf, of spectral type sdM7.0 as well as an earlier type (sdM1.5) star. The latter has an extremely large space velocity with clear halo kinematics. Two objects show featureless spectra typical of cool white dwarfs. One of them is probably a very nearby (d~4pc) thin disk object and may be the nearest isolated white dwarf, the other one has thick disk kinematics.Comment: 9 pages, 4 figures, accepted for publication in Astronomy and Astrophysic

BD+43 3654 -- a blue straggler?

The astrometric data on the runaway star BD+43 3654 are consistent with the origin of this O4If star in the center of the Cyg OB2 association, while BD+43 3654 is younger than the association. To reconcile this discrepancy, we suggest that BD+43 3654 is a blue straggler formed via a close encounter between two tight massive binaries in the core of Cyg OB2. A possible implication of this suggestion is that the very massive (and therefore apparently very young) stars in Cyg OB2 could be blue stragglers as well. We also suggest that the binary-binary encounter producing BD+43 3654 might be responsible for ejection of two high-velocity stars (the stripped helium cores of massive stars) -- the progenitors of the pulsars B2020+28 and B2021+51.Comment: 4 pages, 1 figure, accepted for publication in A&A Letter