Abstract
The star formation (SFH) and chemical enrichment (CEH) histories of Local Group galaxies are traditionally studied by analyzing their resolved stellar populations in a form of ...color–magnitude diagrams obtained with the
Hubble Space Telescope
. Star clusters can be studied in integrated light using ground-based telescopes to much larger distances. They represent snapshots of the chemical evolution of their host galaxy at different ages. Here we present a simple theoretical framework for the chemical evolution based on the instantaneous recycling approximation (IRA) model. We infer a CEH from an SFH and vice versa using observational data. We also present a more advanced model for the evolution of individual chemical elements that takes into account the contribution of supernovae type Ia. We demonstrate that ages, iron, and
α
-element abundances of 15 star clusters derived from the fitting of their integrated optical spectra reliably trace the CEH of the Large Magellanic Cloud obtained from resolved stellar populations in the age range 40 Myr <
t
< 3.5 Gyr. The CEH predicted by our model from the global SFH of the LMC agrees remarkably well with the observed cluster age–metallicity relation. Moreover, the present-day total gas mass of the LMC estimated by the IRA model (
) matches within uncertainties the observed H
i
mass corrected for the presence of molecular gas (
). We briefly discuss how our approach can be used to study SFHs of galaxies as distant as 10 Mpc at the level of detail that is currently available only in a handful of nearby Milky Way satellites.
Analyzer of Spectra for Age Determination (ASAD) is a new package that can easily predict the age and reddening of stellar clusters from their observed optical integrated spectra by comparing them to ...synthesis model spectra. The ages obtained with ASAD are consistent with ages obtained from previous cluster age methods requiring a more rigorous and time-consuming analysis. This package not only provides fast results, but also allows the user to comprehend the accuracy of these results by providing surface plots and spectral plots for all combinations of observations and models. ASAD is available for download on the Web and can be immediately used on both Mac and Windows.
Integrated spectra of star clusters have proven to be accurate tools for obtaining age, metallicity and reddening of extragalactic clusters for which resolved data is not available. In this work we ...investigate the possibility of recovering age spreads of young star clusters (in the range log (age/year) 6.8 to 7.2) using full-spectrum fitting approach and provide the preliminary results using model spectral combinations, in order to examine whether this approach can be used for identifying age-spreads for a grid with combinations of S/N, cluster age and population mass fraction. Our preliminary results show that false age spreads might be obtained when fitting multiple ages using integrated spectra specially for the lower S/N. A more accurate experiment to determine how reliable is the recovery of the input parameters is needed.
Ages of LMC star clusters using asad 2 Asa'd, Randa S.; Vazdekis, Alexandre; Zeinelabdin, Sami
Monthly notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
2
Journal Article
In this paper, we find the ages and metallicities of 8 Large Magellanic Cloud (LMC) star clusters obtained from integrated light spectra and use them to obtain the Chemical Enrichment History of the ...host galaxy. Our results are in good agreement with those obtained from resolved studies. This confirms that this method can be used for far away galaxies for which their star clusters are not resolved.
ABSTRACT
We investigate the precision of the ages and metallicities of 21 000 mock simple stellar populations (SSPs) determined through full-spectrum fitting. The mock SSPs cover an age range of 6.8 ...< log (age/yr) < 10.2, for three wavelength ranges in the optical regime, using both Padova and MIST isochrone models. Random noise is added to the model spectra to achieve S/N ratios between 10 and 100 per wavelength pixel. We find that for S/N ≥ 50, this technique can yield ages of SSPs to an overall precision of ∆log (age/yr)∼01 for ages in the ranges 7.0 ≤ log (age/yr) ≤ 8.3 and 8.9 ≤ log (age/yr) ≤ 9.4. For the age ranges of 8.3 ≤ log (age/yr) ≤ 8.9 and log (age/yr) ≥ 9.5, which have significant flux contributions from asymptotic giant branch and red giant branch stars, respectively, the age uncertainty rises to about ±0.3 dex. The precision of age and metallicity estimation using this method depends significantly on the S/N and the wavelength range used in the fitting. We quantify the systematic differences in age predicted by the MIST and Padova isochrone models, due to their different assumptions about stellar physics in various important (i.e. luminous) phases of stellar evolution, which needs to be taken in consideration when comparing ages of star clusters obtained using these popular models. Knowing the strengths and limitations of this technique is crucial in interpreting the results obtained for real star clusters and for deciding the optimal instrument set-up before performing the observations.
We present an investigation of 84 star clusters in the Large Magellanic Cloud (LMC) galaxy using different broad-band photometric, age-estimation methods. Because of its intermediate distance, the ...LMC is uniquely positioned to compare its clusters that have previously been aged using both resolved photometry colour-magnitude diagrams (CMDs) of the constituent stars and unresolved methods (integrated, broad-band colour photometry). In our comparison between the published CMD ages to three similar, but different methods based on UBV integrated colours, we find poor matches. We attribute this primarily to two things. First, the UBV integrated broad-band ageing methods require matching a cluster with an expected model prediction of the cluster colours as a function of age. The biggest problem we find is that the stellar clusters in our sample do not typically lie on the model line based on their known age and extinction. That is to say, real cluster colours often do not match the model colours and can be found some distance from expected model values. The second issue, which has been previously documented in numerous studies, is the strong degeneracy between age and extinction in the UBV plane. Certainly, providing more photometric bands will reduce degeneracy between age and reddening. Better yet, if extinction can be independently determined, we show that ages from methods based on integrated colours will more closely match those obtained from CMD ages. However, the underlying issue remains. Simple stellar population models often do not accurately represent the colours of real stellar clusters due to the incomplete and stochastic sampling of the stellar mass function in low- and moderate-mass stellar clusters.
ABSTRACT
In this paper we detect double-lined spectroscopic binaries (SB2) in five open clusters: NGC 2243, NGC 2420, NGC 3532, NGC 6253, and NGC 6705 (M 11) using a method based on high values of ...the projected rotational velocity when they are fitted with single star spectral model. Observed spectra were obtained from the European Southern Observatory archive. The method was validated on the sets of synthetic spectra for the single and binary stars. It is able to reliably select spectroscopic binaries without confusing them with single stars, if the components in a binary rotate slowly and the radial velocity separation is sufficiently high. We found 60 SB2 candidates: two in NGC 2243, eight each in NGC 2420 and NGC 3532, 17 in NGC 6253, and 25 in NGC 6705. Comparison with literature confirms 18 of them, thus we found 42 new SB2 candidates.
ABSTRACT
In this fourth paper of a series on the precision of ages of stellar populations obtained through the full-spectrum fitting technique, we present a first systematic analysis that compares ...the age, metallicity, and reddening of star clusters obtained from resolved and unresolved data namely colour–magnitude diagrams (CMDs) and integrated-light spectroscopy using the same sets of isochrones. We investigate the results obtained with both Padova isochrones and MIST isochrones. We find that there generally is a good agreement between the ages derived from CMDs and integrated spectra. However, for metallicity and reddening, the agreement between results from analyses of CMD and integrated spectra is significantly worse. Our results also show that the ages derived with Padova isochrones match those derived using MIST isochrones, both with the full-spectrum fitting technique and the CMD fitting method. However, the metallicity derived using Padova isochrones does not match that derived using MIST isochrones using the CMD method. We examine the ability of the full-spectrum fitting technique in detecting age spreads in clusters that feature the extended main-sequence turnoff (eMSTO) phenomenon using two-population fits. We find that three out of five eMSTO clusters in our sample are best fitted with one single age, suggesting that eMSTOs do not necessarily translate to detectable age spreads in integrated-light studies.
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