The Initial Mass Function of the Orion Nebula Cluster across the H-burning limit

We present a new census of the Orion Nebula Cluster (ONC) over a large field of view (>30'x30'), significantly increasing the known population of stellar and substellar cluster members with precisely determined properties. We develop and exploit a technique to determine stellar effective temperatures from optical colors, nearly doubling the previously available number of objects with effective temperature determinations in this benchmark cluster. Our technique utilizes colors from deep photometry in the I-band and in two medium-band filters at lambda~753 and 770nm, which accurately measure the depth of a molecular feature present in the spectra of cool stars. From these colors we can derive effective temperatures with a precision corresponding to better than one-half spectral subtype, and importantly this precision is independent of the extinction to the individual stars. Also, because this technique utilizes only photometry redward of 750nm, the results are only mildly sensitive to optical veiling produced by accretion. Completing our census with previously available data, we place some 1750 sources in the Hertzsprung-Russel diagram and assign masses and ages down to 0.02 solar masses. At faint luminosities, we detect a large population of background sources which is easily separated in our photometry from the bona fide cluster members. The resulting initial mass function of the cluster has good completeness well into the substellar mass range, and we find that it declines steeply with decreasing mass. This suggests a deficiency of newly formed brown dwarfs in the cluster compared to the Galactic disk population.Comment: 16 pages, 18 figures. Accepted for publication in The Astrophysical Journa

A multi-color optical survey of the orion nebula cluster. II. The H-R diagram

We present a new analysis of the stellar population of the Orion Nebula Cluster (ONC) based on multi-band optical photometry and spectroscopy.We study the color–color diagrams in BVI, plus a narrowband filter centered at 6200 Å, finding evidence that intrinsic color scales valid for main-sequence dwarfs are incompatible with the ONC in the M spectral-type range, while a better agreement is found employing intrinsic colors derived from synthetic photometry, constraining the surface gravity value as predicted by a pre-main-sequence isochrone.We refine these model colors even further, empirically, by comparison with a selected sample of ONC stars with no accretion and no extinction. We consider the stars with known spectral types from the literature, and extend this sample with the addition of 65 newly classified stars from slit spectroscopy and 182 M-type from narrowband photometry; in this way, we isolate a sample of about 1000 stars with known spectral type. We introduce a new method to self-consistently derive the stellar reddening and the optical excess due to accretion from the location of each star in the BVI color–color diagram. This enables us to accurately determine the extinction of the ONC members, together with an estimate of their accretion luminosities. We adopt a lower distance for the Orion Nebula than previously assumed, based on recent parallax measurements. With a careful choice of also the spectral-type–temperature transformation, we produce the new Hertzsprung–Russell diagram of the ONC population, more populated than previous works. With respect to previous works, we find higher luminosity for late-type stars and a slightly lower luminosity for early types. We determine the age distribution of the population, peaking from ~2 to ~3 Myr depending on the model. We study the distribution of the members in the mass–age plane and find that taking into account selection effects due to incompleteness, removes an apparent correlation between mass and age.We derive the initial mass function for low- and intermediate mass members of the ONC, which turns out to be model dependent and shows a turnover at M ≲ 0.2 M_⊙

Analisis Kinerja Dinas Sosial, Pemuda dan Olahraga Kota Semarang dalam Penanganan Masalah Anak Jalanan di Kota Semarang

The research is going to describe and to analyze the performance department social, youths and sports in Semarang and factors that support or detain their performances. Theory that will be used in reasearch are public administration and five dimensions of performance which are productivity, service quality, responsivity, responsibility and accountability with descriptive qualitative study. This research using interview, observation, documentation as method to get information from social services, youth and sports in Semarang and the caretaker of anak emas foundation as the extension hand of the goverment to take care of homeless kids. The result of research is showed that performance of social services, youth and sports in their role to make a better social life for homeless kid is not quite optimal specially in productivity, service quality, and accountability, we see there are some problems in human resources, budgets and lack of information in website also lack of support to another foundation as the extension hand of goverment. However, the performance of department of social, youths and sports had been supported by their ability to discover the street kid's needs through some programs which are better than the previous year and their obedience to rules and SOP also stick to the principles of administrative as they did their job There are some ideas to counter the problem ,for example, raise the budget, add human resources, more concern about another institution and smoother the services

Multichannel cross-layer routing for sensor networks

This paper proposes a new decentralised multi-channel tree building protocol with a centralised controller for the Internet of Things. The protocol alleviates the effect of interference which results in improved network efficiency and stability, and link reliability. The proposal takes into account all available channels to utilise the spectrum and aims to use the spectrum efficiently by transmitting on several channels. The protocol detects which channels suffer interference and changes away from those channels. The algorithm for channel selection is a two-hop colouring protocol that reduces the chances of nearby nodes to transmit on the same channel. All nodes are battery operated except for the low power border router (LPBR). This enables a centralised channel switching process at the LPBR. The protocol is built based on the routing protocol for low power and lossy networks (RPL). In its initial phase, the protocol uses RPL's standard topology formation to create an initial working topology and then seeks to improve this topology by switching channels. The implementation and evaluation of the protocol is performed using the Contiki framework. The experimental results demonstrate an increased resilience to interference and significantly higher throughput making better use of the total available spectrum and link stability

HST measures of Mass Accretion Rates in the Orion Nebula Cluster

The present observational understanding of the evolution of the mass accretion rates (Macc) in pre-main sequence stars is limited by the lack of accurate measurements of Macc over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk evolution. Based on HST/WFPC2 observations, we present a study of Macc for a sample of \sim 700 sources in the Orion Nebula Cluster, ranging from the Hydrogen-burning limit to M\ast \sim 2M\odot. We derive Macc from both the U-band excess and the H{\alpha} luminosity (LH{\alpha}), after determining empirically both the shape of the typical accretion spectrum across the Balmer jump and the relation between the accretion luminosity (Lacc) and LH{\alpha}, that is Lacc/L\odot = (1.31\pm0.03)\cdotLH{\alpha}/L\odot + (2.63\pm 0.13). Given our large statistical sample, we are able to accurately investigate relations between Macc and the parameters of the central star such as mass and age. We clearly find Macc to increase with stellar mass, and decrease over evolutionary time, but we also find strong evidence that the decay of Macc with stellar age occurs over longer timescales for more massive PMS stars. Our best fit relation between these parameters is given by: log(Macc/M\odot\cdotyr)=(-5.12 \pm 0.86) -(0.46 \pm 0.13) \cdot log(t/yr) -(5.75 \pm 1.47)\cdot log(M\ast/M\odot) + (1.17 \pm 0.23)\cdot log(t/yr) \cdot log(M\ast/M\odot). These results also suggest that the similarity solution model could be revised for sources with M\ast > 0.5M\odot. Finally, we do not find a clear trend indicating environmental effects on the accretion properties of the sources.Comment: 17 pages, 15 figures, accepted for publication in Ap

Determinan Voluntary Nonfinancial Disclosure pada Perusahaan di Indonesia

Penelitian ini menjelaskan pengaruh dari ownership structure dan tax disclosure pada voluntary nonfinancial disclosure di Indonesia.Ownership structureterdiri dari public ownership dan foreign ownership. Tax disclosure yang merupakan bagian dari mandatory disclosure. Voluntary nonfinancial disclosure diproksikan oleh jumlah skor dari strategic disclosure, labor disclosure, environment disclosure dan social disclosure. Penelitian ini menjelaskan praktik voluntary nonfinanial disclosure pada annual report Perusahaan yang terdaftar di BEI tahun 2009-2012. Sampel dari penelitian ini adalah 102 Perusahaan yang terdaftar di BEI tahun 2009-2012. Total annual report yang dijadikan sampel adalah 408. Teknik pengambilan sampel menggunakan teknik purposive sampling. Hasil penelitian menunjukan bahwa Foreign ownership, public ownership, tax disclosure, size dan Asset turnover berhubungan dengan voluntary nonfinancial disclosure pada Perusahaan-Perusahaan yang terdaftar di BEI

Quantitative Evidence for an Intrinsic Age Spread in the Orion Nebula Cluster

Aims. We present a study of the distribution of stellar ages in the Orion Nebula Cluster (ONC) based on accurate HST photometry taken from the HST Treasury Program observations of the ONC utilizing the most recent estimate of the cluster's distance (Menten et al. 2007). We investigate the presence of an intrinsic age spread in the region and a possible trend of age with the spatial distribution. Methods. We estimate the extinction and accretion luminosity towards each source by performing synthetic photometry on an empirical calibration of atmospheric models (Da Rio et al. 2010) using the package Chorizos (Maiz-Apellaniz 2004). The position of the sources in the HR-diagram is compared with different theoretical isochrones to estimate the mean cluster age and age dispersion. Through Monte Carlo simulations we quantify the amount of intrinsic age spread in the region, taking into account uncertainties on the distance, spectral type, extinction, unresolved binaries, accretion and photometric variability. Results. According to Siess et al. (2000) evolutionary models the mean age of the Cluster is 2.2 Myr with a scatter of few Myrs. With Monte Carlo simulations we find that the observed age spread is inconsistent with a coeval stellar population, but is in agreement with a star formation activity between 1.5 and 3.5 Myrs. We also observe light evidence for a trend of ages with spatial distribution.Comment: 12 pages, 12 figures, Accepted for publication in Astronomy and Astrophysic