Mapping the Galactic halo with main-sequence and RR Lyrae stars

We present an analysis of Galactic halo structure, substructure, and metallicity traced by mainsequence and RR Lyrae stars selected from the SDSS stripe 82 and CFHT Legacy Survey data sets. The main result of the study based on SDSS stripe 82 data is a 2D map of the Galactic halo that reaches distances of 100 kpc and traces previously known and new halo substructures, such as the Sagittarius and Pisces tidal streams. We present strong direct evidence, based on both RR Lyrae and main-sequence stars, that the halo stellar number density profile significantly steepens beyond 30 kpc from the Galactic center. The steepening of the density profile beyond 30 kpc is also evident in the distribution of main-sequence stars observed by the CFHT Legacy Survey along four Galactic lines of sight. In the two CFHT sightlines where we do not detect significant substructure, the median metallicity is found to be independent of distance within systematic uncertainties ([Fe/H] ∼ −1.5 ± 0.1 dex within 30 kpc of the Galactic Center)

The Shape and Profile of the Milky Way Halo as Seen by the Canada-France-Hawaii Telescope Legacy Survey

We use Canada-France-Hawaii Telescope Legacy Survey data for 170 deg^2, recalibrated and transformed to the Sloan Digital Sky Survey ugri photometric system, to study the distribution of near-turnoff main-sequence stars in the Galactic halo along four lines of sight to heliocentric distances of ~35 kpc. We find that the halo stellar number density profile becomes steeper at Galactocentric distances greater than R_(gal) ~ 28 kpc, with the power-law index changing from n_(inner) = –2.62 ± 0.04 to n_(outer) = –3.8 ± 0.1. In particular, we test a series of single power-law models and find them to be strongly disfavored by the data. The parameters for the best-fit Einasto profile are n = 2.2 ± 0.2 and R_e = 22.2 ± 0.4 kpc. We measure the oblateness of the halo to be q ≡ c/a = 0.70 ± 0.01 and detect no evidence of it changing across the range of probed distances. The Sagittarius stream is detected in the l = 173° and b = –62° direction as an overdensity of [Fe/H] ~ -1.5 dex stars at R_(gal) ~ 32 kpc, providing a new constraint for the Sagittarius stream and dark matter halo models. We also detect the Monoceros stream as an overdensity of [Fe/H] > -1.5 dex stars in the l = 232° and b = 26° direction at R_(gal) ≲ 25 kpc. In the two sight lines where we do not detect significant substructure, the median metallicity is found to be independent of distance within systematic uncertainties ([Fe/H] ~ -1.5 ± 0.1 dex)

The Mass Profile of the Galaxy to 80 kpc

The Hypervelocity Star survey presents the currently largest sample of radial velocity measurements of halo stars out to 80 kpc. We apply spherical Jeans modeling to these data in order to derive the mass profile of the Galaxy. We restrict the analysis to distances larger than 25 kpc from the Galactic center, where the density profile of halo stars is well approximated by a single power law with logarithmic slope between -3.5 and -4.5. With this restriction, we also avoid the complication of modeling a flattened Galactic disk. In the range 25 < r < 80 kpc, the radial velocity dispersion declines remarkably little; a robust measure of its logarithmic slope is between -0.05 and -0.1. The circular velocity profile also declines remarkably little with radius. The allowed range of V_c(80 kpc) lies between 175 and 231 km/s, with the most likely value 193 km/s. Compared with the value at the solar location, the Galactic circular velocity declines by less than 20% over an order of magnitude in radius. Such a flat profile requires a massive and extended dark matter halo. The mass enclosed within 80 kpc is 6.9(+3.0-1.2) 10^11 Msun. Our sample of radial velocities is large enough that the biggest uncertainty in the mass is not statistical but systematic, dominated by the density slope and anisotropy of the tracer population. Further progress requires modeling observed datasets within realistic simulations of galaxy formation.Comment: matches version accepted to ApJ Letter

Halo Velocity Groups in the Pisces Overdensity

We report spectroscopic observations with the Gemini South Telescope of 5 faint V~20 RR Lyrae stars associated with the Pisces overdensity. At a heliocentric and galactocentric distance of ~80 kpc, this is the most distant substructure in the Galactic halo known to date. We combined our observations with literature data and confirmed that the substructure is composed of two different kinematic groups. The main group contains 8 stars and has = 50 km/s, while the second group contains four stars at a velocity of = -52 km/s, where V_{gsr} is the radial velocity in the galactocentric standard of rest. The metallicity distribution of RR Lyrae stars in the Pisces overdensity is centered on [Fe/H]=-1.5 dex and has a width of 0.3 dex. The new data allowed us to establish that both groups are spatially extended making it very unlikely that they are bound systems, and are more likely to be debris of a tidally disrupted galaxy or galaxies. Due to small sky coverage, it is still unclear whether these groups have the same or different progenitors.Comment: 21 pages, 5 figures, 3 tables, accepted to Astrophysical Journa

Basic Characteristics of Bonds and their Dynamics on the Croatian Secondary Market

In light of recent announcements of the Ministry of Finance about the emission of the so-called national bonds, this paper deals with the problems related to bonds as the most widely accepted financial instrument on the Croatian secondary market. Although the meaning of the bond as a debt security financial instrument is probably clear to everyone, trading and utilization of all the advantage this financial instrument offers is still insufficiently developed. Moreover, since bonds appear to be a possible alternative to bank deposits, it is necessary to determine the basic concepts of the difference in the calculation of yield between these two potential investments. Considering these facts, the contribution of this paper is aimed at taking a closer look and simplifying the overall understanding of this significant financial instrument. On top of that, the purpose of this paper is to raise the awareness of the broader public with respect to understanding of the basic characteristics of bonds, their advantages and disadvantages and ultimately to elaborate in detail the investment possibilities offered by bonds, as one of the most popular debt security financial instrument in Croatia. The first chapter describes the general problems related to bonds, their basic characteristics and current divisions. The paper then elaborates current dynamics of bonds in the secondary capital market in the Republic of Croatia, providing a comparative presentation of purchase and sale trade channels in the secondary market. The final chapter shows a practical example of price and yield calculation until maturity of the bond issued by the Ministry of Finance of RoC, being traded on Zagreb Stock Exchange

Influence and character of surface water in Maksimir park

Park Maksimir je sagrađen u 19. st., i od tada plijeni pozornost zbog svoje estetike, načina građenja ali i kulturne i ekološke raznolikosti. Svakodnevno, bez obzira na godišnja doba možemo vidjeti različite ljude kako dolaze u park sa različitim interesima, neki dolaze proučavati floru i faunu parka, neki ljudi dolaze zbog rekreacije a neki samo zbog odmora. U sklopu parka Maksimir nalazi se i Zoološki vrt koji rado posjećuju mladi ali i stariji ljudi, kako bi naučili neke nove stvari o životinjskom svijetu. Osim Zoološkog vrta veliku pozornost privlače i maksimirska jezera koja svakom čovjeku izvlači divljenje ili barem uzdah. Iako dosta blizu centra grada, park Maksimir predstavlja zaista jedno kulturno, povijesno i ekološko bogatstvo. No proučavajući malo bolje sam park nije sve tako bajno kako se čini. Premda je park zaštićen, ljudi odlažu smeće na puteljke, bacaju na livade, grmove, pa čak i ju jezera. Proučavajući park i tu ljepotu prirode čovjek veoma lako može uočiti kako postoji određeni stupanj eutrofikacije u jezerima. Pretpostavlja se da dolazi do eutrofikacije zbog prirodnog ali i antropogenog utjecaja. Pitanje je samo koliko to 'onečišćenje' utječe na samu floru i faunu jezera ali i samog parka. Danas postoji nekoliko veoma uspješnih metoda pročišćavanja jezera, tako da sumnjam da će se situacija u jezerima i okolišu pogoršati, dapače očekujem suprotno.Maksimir Park was built in the 19th century, and from that period he's gathering attention because of his esthetic, the way it was built but also because of the cultural and ecological variety. Every day, no matter the season, we can see different people walking in the park with different interests, some of them are coming to explore the flora and fauna, some because of the recreation and some people just want to relax. In the complex of Makismir Park is the ZOO which gathers all kindds of people who want to learn more about the animal world. Except from the ZOO, the lakes of Maksimir also attracts big attention and leaves some people fully surprised and admired. Although Maksimir is near the centre of the city it presents a big cultural, historical and ecological wealth. After carefully studying the park not everything is all that good. Althought the park is protected, every day people throw their garbage on the sidewalks, meadows, bushes and even in the lakes. Examining the park and the beauty of nature, we can very easy see that there is a significant grade of euphrofication in the lakes. The presumption is that the euphrofication is caused by natural and anthropogenic influence. The question is how that 'pollution' affects the flora and fauna of the lakes and the whole park. Today we know a few successful methods of purification the lakes so I don't doubt that the conditions of lakes and the nature will get any worse, infact I expect the opposite

Quasar Selection Based on Photometric Variability

We develop a method for separating quasars from other variable point sources using SDSS Stripe 82 light curve data for ~10,000 variable objects. To statistically describe quasar variability, we use a damped random walk model parametrized by a damping time scale, tau, and an asymptotic amplitude (structure function), SF_inf. With the aid of an SDSS spectroscopically confirmed quasar sample, we demonstrate that variability selection in typical extragalactic fields with low stellar density can deliver complete samples with reasonable purity (or efficiency, E). Compared to a selection method based solely on the slope of the structure function, the inclusion of the tau information boosts E from 60% to 75% while maintaining a highly complete sample (98%) even in the absence of color information. For a completeness of C=90%, E is boosted from 80% to 85%. Conversely, C improves from 90% to 97% while maintaining E=80% when imposing a lower limit on tau. With the aid of color selection, the purity can be further boosted to 96%, with C= 93%. Hence, selection methods based on variability will play an important role in the selection of quasars with data provided by upcoming large sky surveys, such as Pan-STARRS and the Large Synoptic Survey Telescope (LSST). For a typical (simulated) LSST cadence over 10 years and a photometric accuracy of 0.03 mag (achieved at i~22), C is expected to be 88% for a simple sample selection criterion of tau>100 days. In summary, given an adequate survey cadence, photometric variability provides an even better method than color selection for separating quasars from stars.Comment: (v2) 50 pages, accepted to Ap