scholarly journals Distances and ages of globular clusters

2007 ◽  
Vol 3 (S248) ◽  
pp. 440-442 ◽  
Author(s):  
B. Chaboyer
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Formation History ◽  
Minimum Age ◽  
History Of ◽  
The Mean ◽  
Age Of The Universe ◽  
The Universe ◽  
Age Determinations

AbstractAs the oldest objects whose ages can be accurately determined, Galactic globular clusters can be used to establish the minimum age of the universe (and hence, to constrain cosmological models) and to study the early formation history of the Milky Way. The largest uncertainty in the determination of globular cluster ages is the distance scale. The current uncertainty in the distances to globular clusters is ~ 6%, which leads to a 13% uncertainty in the absolute ages of globular clusters. I am the PI on a SIM-Planetquest key project to determine the distances of 21 globular clusters with an accuracy of ranging from 1 to 4%. This will lead to age determinations accurate to 5 − 9%. The mean age of the oldest, most metal-poor globular clusters will be determined with an accuracy of ±3%.

scholarly journals Hipparcos subdwarfs and globular cluster ages: towards reliable absolute ages

1997 ◽  
Vol 189 ◽  
pp. 433-438 ◽  
Author(s):  
F. Pont ◽  
M. Mayor ◽  
C. Turon
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Large Fraction ◽  
Age Determination ◽  
Colour Scale ◽  
Minimum Age ◽  
Age Of The Universe ◽  
Robust Prediction ◽  
The Universe ◽  
Cluster Age

The maximum age of galactic globular clusters provides the best observational constraint on the minimum age of the Universe. One of the main “missing link” in the globular cluster age determination has been the lack of a precise calibration, with local subdwarfs, of the position of the subdwarf sequence at different [Fe/H].Hipparcos data may change this situation. As many precise parallaxes become available for local subdwarfs, the distance to globular clusters can be estimated directly from ZAMS fitting to the subdwarf locus. The ages can then be inferred from the turnoff luminosity (a robust prediction of stellar evolution models), rather than using secondary indicators such as Horizontal-Branch position, or indicators depending on the uncertain colour scale such as turnoff colour.Combining Hipparcos parallaxes with [Fe/H] values determined with the CORAVEL spectrometer, we are studying the position of the subdwarfs in the Colour-Magnitude Diagram from a sample of more than 900 subdwarf candidates. Preliminary results are presented here. It is shown that the distances of many subdwarfs had been underestimated in previous studies, mainly because a large fraction of them is in fact evolved off the main sequence into the turnoff or the subgiant branch.

scholarly journals Cosmic Star Formation from the Milky Way and its Satellites

1999 ◽  
Vol 190 ◽  
pp. 8-14
Author(s):  
F.D.A. Hartwick
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Evolutionary Models ◽  
Disk Mass ◽  
Formation History ◽  
History Of ◽  
The Universe

We use observations and evolutionary models of local objects to interpret a recent determination of the star-formation history of the universe. By fitting the global star-formation rate, the model predicts the ratio of spheroid to disk mass of ~1, an intergalactic medium (IGM) whose mass is ~2.3 times the mass in stars, and whose metallicity is ~0.1 Z⊙.

scholarly journals Observations of GRBs at high redshift

2007 ◽  
Vol 365 (1854) ◽  
pp. 1377-1384 ◽  
Author(s):  
Nial R Tanvir ◽  
Páll Jakobsson
Keyword(s):  
Gamma Ray ◽  
High Redshift ◽  
Cosmological Parameters ◽  
Gamma Ray Bursts ◽  
Star Formation History ◽  
Redshift Distribution ◽  
Formation History ◽  
History Of ◽  
The Universe

The extreme luminosity of gamma-ray bursts and their afterglows means they are detectable, in principle, to very high redshifts. Although the redshift distribution of gamma-ray bursts (GRBs) is difficult to determine, due to incompleteness of present samples, we argue that for Swift-detected bursts, the median redshift is between 2.5 and 3, with a few per cent probably at z >6. Thus, GRBs are potentially powerful probes of the era of reionization and the sources responsible for it. Moreover, it seems probable that they can provide constraints on the star-formation history of the Universe and may also help in the determination of the cosmological parameters.

scholarly journals Globular Cluster Ages from Hipparcos Subdwarfs

1999 ◽  
Vol 183 ◽  
pp. 69-69
Author(s):  
F. Pont ◽  
D.A. Vandenberg ◽  
M. Mayor ◽  
C. Turon
Keyword(s):  
Stellar Evolution ◽  
Globular Clusters ◽  
Direct Sequence ◽  
Reliable Determination ◽  
Upper Limit ◽  
Minimum Age ◽  
The Difference ◽  
The Universe ◽  
Hipparcos Parallax

The new Hipparcos parallax data for local subdwarfs allow a much more reliable determination of the distance to globular clusters (by direct sequence fitting) than was previously possible. Earlier studies (Reid 1997, Gratton et al. 1997) have reported larger distances than expected, especially for the most metal-poor clusters, implying much younger ages. In our study of Hipparcos subdwarfs applied to M92 — representative of the oldest, most metal-poor clusters — we find however a distance only slightly in excess of previous expectations. We show, using Monte Carlo simulations, that most of the difference may be explained by our more detailed treatment of the Lutz-Kelker and selection biases. With up-to-date stellar evolution models, we derive a minimum age of 13 Gyr for the Universe. This value, although lower than previous estimates, still imposes a rather strict upper limit to Ho in the context of standard cosmological models.

scholarly journals On the merger origin of nuclear star clusters

2016 ◽  
Vol 11 (S321) ◽  
pp. 117-119
Author(s):  
Athanasia Tsatsi ◽  
Alessandra Mastrobuono-Battisti
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Star Clusters ◽  
Fine Tuning ◽  
Physical Processes ◽  
Formation History ◽  
History Of ◽  
Kinematic Properties

AbstractNuclear Star Clusters (NSCs) are commonly observed in the centers of most galaxies, including our Milky Way (MW). While their study can reveal important information about the innermost regions of galaxies, the physical processes regulating their formation are still poorly understood. We explore a possible merger origin of NSCs by studying direct N-body simulations of globular clusters (GCs) that are initially randomly distributed in the outskirts and consecutively infall to the center of a MW-like nuclear bulge. We find that the NSC that forms through this process shows a significant amount of rotation, and both morphological and kinematic properties are comparable with observations of the MW NSC. We show that no fine-tuning of the orientation of the infalling GCs is necessary to result in a rotating NSC. This study shows the plausibility of the cluster infall scenario and can help towards setting better constraints to the formation history of NSCs.

scholarly journals In Situ exploration of the giant planets

2021 ◽  
Author(s):  
O. Mousis ◽  
D. H. Atkinson ◽  
R. Ambrosi ◽  
S. Atreya ◽  
D. Banfield ◽  
...  
Keyword(s):  
Solar System ◽  
Giant Planets ◽  
Atmospheric Composition ◽  
Formation History ◽  
History Of ◽  
Composition Structure ◽  
Galileo Probe ◽  
Probe Measurements

AbstractRemote sensing observations suffer significant limitations when used to study the bulk atmospheric composition of the giant planets of our Solar System. This impacts our knowledge of the formation of these planets and the physics of their atmospheres. A remarkable example of the superiority of in situ probe measurements was illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases’ abundances and the precise measurement of the helium mixing ratio were only made available through in situ measurements by the Galileo probe. Here we describe the main scientific goals to be addressed by the future in situ exploration of Saturn, Uranus, and Neptune, placing the Galileo probe exploration of Jupiter in a broader context. An atmospheric entry probe targeting the 10-bar level would yield insight into two broad themes: i) the formation history of the giant planets and that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. An atmospheric probe could represent a significant ESA contribution to a future NASA New Frontiers or flagship mission to be launched toward Saturn, Uranus, and/or Neptune.

scholarly journals Gaia DR1 completeness within 250 pc & star formation history of the Solar neighbourhood

2017 ◽  
Vol 12 (S330) ◽  
pp. 148-151 ◽  
Author(s):  
Edouard J. Bernard
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Solar Neighbourhood ◽  
The Sun ◽  
Thick Disc ◽  
Formation History ◽  
Magnitude Diagram ◽  
History Of

AbstractWe took advantage of the Gaia DR1 to combine TGAS parallaxes with Tycho-2 and APASS photometry to calculate the star formation history (SFH) of the solar neighbourhood within 250 pc using the colour-magnitude diagram fitting technique. We present the determination of the completeness within this volume, and compare the resulting SFH with that calculated from the Hipparcos catalogue within 80 pc of the Sun. We also show how this technique will be applied out to ~5 kpc thanks to the next Gaia data releases, which will allow us to quantify the SFH of the thin disc, thick disc and halo in situ, rather than extrapolating based on the stars from these components that are today in the solar neighbourhood.

scholarly journals Hidden infrared star clusters in our Galaxy: follow-up observations

2009 ◽  
Vol 5 (S266) ◽  
pp. 366-366
Author(s):  
Jura Borissova ◽  
Radostin Kurtev ◽  
Margaret M. Hanson ◽  
Leonid Georgiev ◽  
Valentin Ivanov ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Star Cluster ◽  
Open Clusters ◽  
Star Formation History ◽  
Stellar Disk ◽  
Physical Parameters ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Infrared Star

AbstractWe are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to guide models seeking to understand the structure and recent star-formation history of our Galaxy. The immediate goal is to derive accurate cluster physical parameters using precise infrared photometry and spectroscopy. So far, we observed approximately 60 star cluster candidates selected from different infrared catalogs. Their nature, reddening, distance, age and mass are analyzed. Two of them, Mercer 3 and Mercer 5, are new obscured Milky Way globular clusters. Among the newly identified open clusters, the objects [DBS2003] 179, Mercer 23, Mercer 30, Mercer 70, and [DBS2003] 106 are particularly interesting because they contain massive young OB and Wolf–Rayet stars with strong emission lines.

scholarly journals Did the Bulge Form All at Once?

1996 ◽  
Vol 169 ◽  
pp. 403-410
Author(s):  
R.M. Rich
Keyword(s):  
Galaxy Evolution ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Field Population ◽  
Dynamical Instability ◽  
Galactic Bulge ◽  
Recent Developments ◽  
Order Of Magnitude ◽  
History Of

It is reasonable to say that if Jan Oort were alive today, he would no doubt find recent developments in the study of the Galactic bulge to be fascinating. Oort considered the Galactic bulge in two contexts. First, he was interested in the use of the RR Lyrae stars as probes to determine the distance to the Galactic Center. No doubt, Oort would have been excited about the growing evidence of the bulge's triaxiality, as well as by the debate over the age of the bulge. His second interest was in the nature of activity at the center, an issue that I will not discuss in this review. The latter also remains an unsolved problem of the Milky Way, and (based on his work) one that might have been nearer to his heart than this one. Yet the question of when the bulge formed is ultimately a question about the formation history of the Galaxy. The oldest stars (those whose ages we are certain of) are found in Galactic globular clusters, the sum total of which are ≈ 5 × 107M⊙. The field population of the bulge is ≈ 2–3 × 1010M⊙, an order of magnitude more massive than the field population of the metal poor spheroid. So if the bulge formed all at once, and early, then the Milky Way had a luminous, even cataclysmic youth. But if the bulge formed later in the history of our galaxy, as a starburst or dynamical instability of the central disk, then the young Milky Way may have been inconspicuous and primeval galaxies may be hard to find indeed. If our bulge formed very early, its stellar population might have much in common with the giant ellipticals, while a late bulge might teach us much about processes that affect galaxy evolution.

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