Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStar Cluster Analyses from Multi-Band Photometry: the Key Advantage of SALTs U-band Sensitivity
35
0
0.0
(
0
)
Added by
Uta Fritze - v.Alvensleben
Publication date
2006
fields
Physics
and research's language is
English
Authors
Uta Fritze - v. Alvensleben
Ask ChatGPT about the research
No Arabic abstract
Conventionally, CMD analyses of nearby star clusters are based on observations in 2 passbands. They are plagued by considerable degeneracies between age, metallicity, distance (and extinction) that can largely be resolved by including additional passbands with U being most appropriate for young SCs and I or a NIR band for old globular clusters. For star clusters that cannot be resolved, integrated photometry in suitably selected passbands was shown to be as accurate as spectroscopy in independently revealing ages, metallicities, internal extinction, and photometric masses and their respective 1 sigma uncertainties, when analysed with a dedicated analysis tool for their Spectral Energy Distributions (SEDs) (cf. Anders et al. 2004a, b, de Grijs et al. 2003b). For external galaxies, rich star cluster populations can thus be efficiently analysed using deep exposures in 4 suitable filters. Again, the inclusion of the U-band significantly reduces the uncertainties in the cluster parameters. The age and metallicity distributions of star cluster systems yield valuable information about the formation history of their parent galaxies (Fritze - v. A. 2004). Here, we present our GALEV evolutionary synthesis models for star clusters of various metallicities (Anders, Fritze - v. A. 2003), recently extended to include the time evolution of CMDs, the dedicated SED Analysis Tool AnalySED we developed, show results on the basis of HST data, and present first data for a young star cluster system in the ongoing spiral-spiral merger NGC 1487 obtained with SALT during the SALTICAM Performance Verification Phase.
rate research
Read More
A new method of determining galaxy star-formation histories (SFHs) is presented. Using the method, the feasibility of recovering SFHs with multi-band photometry is investigated. The method divides a galaxys history into discrete time intervals and reconstructs the average rate of star formation in each interval. This directly gives the total stellar mass. A simple linear inversion solves the problem of finding the most likely discretised SFH for a given set of galaxy parameters. It is shown how formulating the method within a Bayesian framework lets the data simultaneously select the optimal regularisation strength and the most appropriate number of discrete time intervals for the reconstructed SFH. The method is demonstrated by applying it to mono-metallic synthetic photometric catalogues created with different input SFHs, assessing how the accuracy of the recovered SFHs and stellar masses depend on the photometric passband set, signal-to-noise and redshift. The results show that reconstruction of SFHs using multi-band photometry is possible, being able to distinguish an early burst of star formation from a late one, provided an appropriate passband set is used. Although the resolution of the recovered SFHs is on average inferior compared to what can be achieved with spectroscopic data, the multi-band approach can process a significantly larger number of galaxies per unit exposure time.
This paper presents CCD multicolour photometry for the old open cluster NGC 188. The observations were carried out as a part of the Beijing--Arizona--Taiwan--Connecticut Multicolour Sky Survey from 1995 February to 2008 March, using 15 intermediate-band filters covering 3000--10000 AA. By fitting the Padova theoretical isochrones to our data, the fundamental parameters of this cluster are derived: an age of $t=7.5pm 0.5$ Gyr, a distant modulus of $(m-M)_0=11.17pm0.08$, and a reddening of $E(B-V)=0.036pm0.010$. The radial surface density profile of NGC 188 is obtained by star count. By fitting the King model, the structural parameters of NGC 188 are derived: a core radius of $R_{c}=3.80$, a tidal radius of $R_{t}=44.78$, and a concentration parameter of $C_{0}=log(R_{t}/R_{c})=1.07$. Fitting the mass function to a power-law function $phi(m) propto m^{alpha}$, the slopes of mass functions for different spatial regions are derived. We find that NGC 188 presents a slope break in the mass function. The break mass is $m_{rm break}=0.885~M_{odot}$. In the mass range above $m_{rm break}$, the slope of the overall region is $alpha=-0.76$. The slope of the core region is $alpha=1.09$, and the slopes of the external regions are $alpha=-0.86$ and $alpha=-2.15$, respectively. In the mass range below $m_{rm break}$, these slopes are $alpha=0.12$, $alpha=4.91$, $alpha=1.33$, and $alpha=-1.09$, respectively. The mass segregation in NGC 188 is reflected in the obvious variation of the slopes in different spatial regions of this cluster.
We present here multi-band photometry for over 2000 Main-belt asteroids. For each target we report the probabilistic taxonomy using the measured V-R and V-I colors in combination with a machine-learning generated decision surface in color-color space. Through this method we classify >85% of our targets as one the four main Bus-DeMeo complexes: S-, C-, X-, or D-type. Roughly one third of our targets have a known associated dynamic family with 69 families represented in our data. Within uncertainty our results show no discernible difference in taxonomic distribution between family members and non-family members. Nine of the 69 families represented in our observed sample had 20 or more members present and therefore we investigate the taxonomy of these families in more detail and find excellent agreement with literature. Out of these 9 well-sampled families, our data show that the Themis, Koronis, Hygiea, Massalia, and Eunomia families display a high degree of taxonomic homogeneity and that the Vesta, Flora, Nysa-Polana, and Eos families show a significant level of mixture in taxonomies. Using the taxonomic purity and the degree of dispersion in observed colors for each of the 9 well-sampled collisional families we also speculate which of these families potentially originated from a differentiated parent body and/or is a family with a possible undetermined nested family. Additionally, we obtained sufficient photometric data for 433 of our targets to extract reliable rotation periods and observe no obvious correlation between rotation properties and family membership.
Ground-based exoplanet surveys such as SuperWASP, HATNet and KELT have discovered close to two hundred transiting extrasolar planets in the past several years. The strategy of these surveys is to look at a large field of view and measure the brightnesses of its bright stars to around half a percent per point precision, which is adequate for detecting hot Jupiters. Typically, these surveys use CCD detectors to achieve high precision photometry. These CCDs, however, are expensive relative to other consumer-grade optical imaging devices, such as digital single-lens reflex cameras (DSLRs). We look at the possibility of using a digital single-lens reflex camera for precision photometry. Specifically, we used a Canon EOS 60D camera that records light in 3 colors simultaneously. The DSLR was integrated into the HATNet survey and collected observations for a month, after which photometry was extracted for 6600 stars in a selected stellar field. We found that the DSLR achieves a best-case median absolute deviation (MAD) of 4.6 mmag per 180 s exposure when the DSLR color channels are combined, and 1000 stars are measured to better than 10 mmag (1%). Also, we achieve 10,mmag or better photometry in the individual colors. This is good enough to detect transiting hot Jupiters. We performed a candidate search on all stars and found four candidates, one of which is KELT-3b, the only known transiting hot Jupiter in our selected field. We conclude that the Canon 60D is a cheap, lightweight device capable of useful photometry in multiple colors.
Our aim in this work is to answer, using simulated narrow-band photometry data, the following general question: What can we learn about galaxies from these new generation cosmological surveys? For instance, can we estimate stellar age and metallicity distributions? Can we separate star-forming galaxies from AGN? Can we measure emission lines, nebular abundances and extinction? With what precision? To accomplish this, we selected a sample of about 300k galaxies with good S/N from the SDSS and divided them in two groups: 200k objects and a template library of 100k. We corrected the spectra to $z = 0$ and converted them to filter fluxes. Using a statistical approach, we calculated a Probability Distribution Function (PDF) for each property of each object and the library. Since we have the properties of all the data from the {sc starlight}-SDSS database, we could compare them with the results obtained from summaries of the PDF (mean, median, etc). Our results shows that we retrieve the weighted average of the log of the galaxy age with a good error margin ($sigma approx 0.1 - 0.2$ dex), and similarly for the physical properties such as mass-to-light ratio, mean stellar metallicity, etc. Furthermore, our main result is that we can derive emission line intensities and ratios with similar precision. This makes this method unique in comparison to the other methods on the market to analyze photometry data and shows that, from the point of view of galaxy studies, future photometric surveys will be much more useful than anticipated.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
