Wide-Field Survey of Emission-line Stars in IC 1396

We have made an extensive survey of emission-line stars in the IC 1396 HII region to investigate the low-mass population of pre-main sequence (PMS) stars. A total of 639 H-alpha emission-line stars were detected in an area of 4.2 deg^2 and their i'-photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the HII region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the HII region. Based on the extinction estimated from the near-infrared (NIR) color-color diagram, we have selected pre-main sequence star candidates associated with IC 1396. The age and mass were derived from the extinction corrected color-magnitude diagram and theoretical pre-main sequence tracks. Most of our PMS candidates have ages of < 3 Myr and masses of 0.2-0.6 Mo. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered to form many low-mass stars at the dense inhomogeneity in and around the HII region by a radiation-driven implosion.Comment: 48 pages, 12 figures, 5 tables, accepted for publication in A

The Elephant Trunk Nebula and the Trumpler 37 cluster: Contribution of triggered star formation to the total population of an HII region

Rich young stellar clusters produce HII 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 (a.k.a., 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 toward the primary ionizing star HD 206267 is found. We argue that the TSF mechanism in IC 1396A is the radiation-driven implosion process persisting over several million years. Analysis of the X-ray luminosity and initial mass functions indicates that >140 stars down to 0.1 Msun were formed by TSF. Considering other BRCs in the IC 1396 HII region, we estimate the TSF contribution for the entire HII region exceeds 14-25% today, and may be higher over the lifetime of the HII region. Such triggering on the periphery of HII regions may be a significant mode of star formation in the Galaxy.Comment: Accepted for publication in MNRAS; 28 pages, 18 figure

A comprehensive framework for the activation, management, and evaluation of Co-production in the public sector

Co-production analyses the practices in which state or firms and lay actors work together in any phase of the production cycle. In the public sector, citizens are not seen as mere recipients of services but as co-producers at different stages. Scholarly interest in co-production has grown steadily in the past years. However, the research has yet to integrate the many co-production concepts into a distinctive theoretical comprehensive framework able to strengthen the understanding of the interrelated dynamics at play. The article conducts a systematic in- depth qualitative review of the co-production literature for the public sector. The results highlight the main components into four pillars of a comprehensive theoretical framework to guide scholars and practitioners in the activation and management of co-production as well as in the evaluation of its outcomes. The article concludes by formulating a future research agenda for co-production in the public sector

Protoplanetary Disk Evolution around the Triggered Star Forming Region Cepheus B

The Cepheus B (CepB) molecular cloud and a portion of the nearby CepOB3b OB association, one of the most active regions of star formation within 1 kpc, have been observed with the IRAC detector on board the Spitzer Space Telescope. The goals are to study protoplanetary disk evolution and processes of sequential triggered star formation in the region. Out of ~400 pre-main sequence (PMS) stars selected with an earlier Chandra X-ray Observatory observation, 95% are identified with mid-infrared sources and most of these are classified as diskless or disk-bearing stars. The discovery of the additional >200 IR-excess low-mass members gives a combined Chandra+Spitzer PMS sample complete down to 0.5 Mo outside of the cloud, and somewhat above 1 Mo in the cloud. Analyses of the nearly disk-unbiased combined Chandra+Spitzer selected stellar sample give several results. Our major finding is a spatio-temporal gradient of young stars from the hot molecular core towards the primary ionizing O star HD 217086. This strongly supports the radiation driven implosion (RDI) model of triggered star formation in the region. The empirical estimate for the shock velocity of 1 km/s is very similar to theoretical models of RDI in shocked molecular clouds...ABRIDGED... Other results include: 1. agreement of the disk fractions, their mass dependency, and fractions of transition disks with other clusters; 2. confirmation of the youthfulness of the embedded CepB cluster; 3. confirmation of the effect of suppression of time-integrated X-ray emission in disk-bearing versus diskless systems.Comment: Accepted for publication in The Astrophysical Journal. 48 pages, 14 figures. For a version with high-quality figures, see http://www.astro.psu.edu/users/gkosta/RESEARCH/cepb_spitzer_chandra.pd

MBM 12: young protoplanetary discs at high galactic latitude

(abridged) We present Spitzer infrared observations to constrain disc and dust evolution in young T Tauri stars in MBM 12, a star-forming cloud at high latitude with an age of 2 Myr and a distance of 275 pc. The region contains 12 T Tauri systems, with primary spectral types between K3 and M6; 5 are weak-line and the rest classical T Tauri stars. We first use MIPS and literature photometry to compile spectral energy distributions for each of the 12 members in MBM 12, and derive their IR excesses. The IRS spectra are analysed with the newly developed two-layer temperature distribution (TLTD) spectral decomposition method. For the 7 T Tauri stars with a detected IR excess, we analyse their solid-state features to derive dust properties such as mass-averaged grain size, composition and crystallinity. We find a spatial gradient in the forsterite to enstatite range, with more enstatite present in the warmer regions. The fact that we see a radial dependence of the dust properties indicates that radial mixing is not very efficient in the discs of these young T Tauri stars. The SED analysis shows that the discs in MBM 12, in general, undergo rapid inner disc clearing, while the binary sources have faster discevolution. The dust grains seem to evolve independently from the stellar properties, but are mildly related to disc properties such as flaring and accretion rates.Comment: 14 pages, accepted by Astronomy and Astrophysic

Geometry of phase separation

We study the domain geometry during spinodal decomposition of a 50:50 binary mixture in two dimensions. Extending arguments developed to treat non-conserved coarsening, we obtain approximate analytic results for the distribution of domain areas and perimeters during the dynamics. The main approximation is to regard the interfaces separating domains as moving independently. While this is true in the non-conserved case, it is not in the conserved one. Our results can therefore be considered as a first-order approximation for the distributions. In contrast to the celebrated Lifshitz-Slyozov-Wagner distribution of structures of the minority phase in the limit of very small concentration, the distribution of domain areas in the 50:50 case does not have a cut-off. Large structures (areas or perimeters) retain the morphology of a percolative or critical initial condition, for quenches from high temperatures or the critical point respectively. The corresponding distributions are described by a $c A^{-\tau}$ tail, where $c$ and $\tau$ are exactly known. With increasing time, small structures tend to have a spherical shape with a smooth surface before evaporating by diffusion. In this regime the number density of domains with area $A$ scales as $A^{1/2}$, as in the Lifshitz-Slyozov-Wagner theory. The threshold between the small and large regimes is determined by the characteristic area, ${\rm A} \sim [\lambda(T) t]^{2/3}$. Finally, we study the relation between perimeters and areas and the distribution of boundary lengths, finding results that are consistent with the ones summarized above. We test our predictions with Monte Carlo simulations of the 2d Ising Model.Comment: 10 pages, 8 figure

High-Resolution Spectroscopy in Tr37: Gas Accretion Evolution in Evolved Dusty Disks

Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R~34,000) spectra in the Halpha region for a large number of stars in the 4 Myr-old cluster Tr 37, containing 146 previously known members and 26 newly identified ones. We present the Halpha line profiles of all members, compare them to our IR observations of dusty disks (2MASS/JHK + IRAC + MIPS 24 micron), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with Halpha equivalent widths smaller than the canonical limit separating CTTS and WTTS. The number of strong accretors appears to be lower than in younger regions, and a large number of CTTS have very small accretion rates (dM/dt<10^{-9} Msun/yr). Taking into account that the spectral energy distributions are consistent with dust evolution (grain growth/settling) in the innermost disk, this suggests a parallel evolution of the dusty and gaseous components. We also observe that about half of the "transition objects" (stars with no IR excesses at wavelengths shorter than ~6 micron) do not show any signs of active accretion, whereas the other half is accreting with accretion rates <10^{-9} Msun/yr. These zero or very low accretion rates reveal important gas evolution and/or gas depletion in the innermost disk, which could be related to grain growth up to planetesimal or even planet sizes. Finally, we examine the rotational velocities of accreting and non accreting stars, finding no significant differences that could indicate disk locking at these ages.Comment: 51 pages, 13 (reduced resolution) figures, 2 tables. AJ in pres

Timescale of Mass Accretion in Pre-Main-Sequence Stars

We present initial result of a large spectroscopic survey aimed at measuring the timescale of mass accretion in young, pre-main-sequence stars in the spectral type range K0 - M5. Using multi-object spectroscopy with VIMOS at the VLT we identified the fraction of accreting stars in a number of young stellar clusters and associations of ages between 1 - 50 Myr. The fraction of accreting stars decreases from ~60% at 1.5 - 2 Myr to ~2% at 10 Myr. No accreting stars are found after 10 Myr at a sensitivity limit of $10^{-11}$ Msun yr-1. We compared the fraction of stars showing ongoing accretion (f_acc) to the fraction of stars with near-to-mid infrared excess (f_IRAC). In most cases we find f_acc < f_IRAC, i.e., mass accretion appears to cease (or drop below detectable level) earlier than the dust is dissipated in the inner disk. At 5 Myr, 95% of the stellar population has stopped accreting material at a rate of > 10^{-11} Msun yr-1, while ~20% of the stars show near-infrared excess emission. Assuming an exponential decay, we measure a mass accretion timescale (t_acc) of 2.3 Myr, compared to a near-to-mid infrared excess timescale (t_IRAC) of 2.9 Myr. Planet formation, and/or migration, in the inner disk might be a viable mechanism to halt further accretion onto the central star on such a short timescale.Comment: Accepted for publicatio

Understanding the need for novelty from the perspective of self-determination theory

A fundamental tenet of self-determination theory is that the satisfaction of three basic, innate psychological needs for autonomy, competence, and relatedness is necessary for optimal functioning. The aim of this research was to propose novelty as a basic psychological need in self-determination theory and develop a new measure to assess novelty need satisfaction, the Novelty Need Satisfaction Scale (NNSS). Two studies were performed, one at the global lifestyle level (Study 1: general adults, N = 399, Mage = 31.30 years) and the other at a contextual level in physical education (Study 2: first-year post-compulsory secondary school students, N = 1035, Mage = 16.20 years). Participants completed the NNSS alongside measures of psychological needs and regulation styles from self-determination theory and psychological well-being. The six-item NNSS showed adequate psychometric properties and discriminant validity with other psychological needs in both studies. Novelty need satisfaction predicted life satisfaction (Study 1) and intrinsic motivation in physical education (Study 2) independent of the other three psychological needs. Results provide preliminary evidence that need for novelty is a unique candidate need alongside existing needs from self-determination theory, but further confirmatory and experimental research is required

Evolution of Galaxy Star Formation and Metallicity: Impact on Double Compact Object Mergers

In this paper, we study the impact of different galaxy statistics and empirical metallicity scaling relations on the merging rates and properties of compact object binaries. Firstly, we analyze the similarities and differences of using the star formation rate functions versus stellar mass functions as galaxy statistics for the computation of cosmic star formation rate density. We then investigate the effects of adopting the Fundamental Metallicity Relation versus a classic Mass Metallicity Relation to assign metallicity to galaxies with given properties. We find that when the Fundamental Metallicity Relation is exploited, the bulk of the star formation occurs at relatively high metallicities, even at high redshift; the opposite holds when the Mass Metallicity Relation is employed, since in this case the metallicity at which most of the star formation takes place strongly decreases with redshift. We discuss the various reasons and possible biases giving rise to this discrepancy. Finally, we show the impact of these different astrophysical prescriptions on the merging rates and properties of compact object binaries; specifically, we present results for the redshift-dependent merging rates and for the chirp mass and time delay distributions of the merging binaries