Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Lithium Age for the Young Cluster IC2391
98
0
0.0
(
0
)
Added by
David Barrado y Navascues
Publication date
1999
fields
Physics
and research's language is
English
Authors
D. Barrado y Navascues n MPIA
Ask ChatGPT about the research
No Arabic abstract
We have identified a large number of possible very low mass members of the cluster IC2391 based primarily on their location in an I versus (R-I)_C CM diagram. We have obtained new photometry and low resolution ($Delta lambda = 2.7$ AA) spectroscopy of 19 of these objects (14.9 $le$ I_C $le$ 17.5) in order to confirm cluster membership. We identify 15 of our targets as likely cluster members based on their spectral types, radial velocity, EW(NaI8200AA), and H(alpha) emission strengths. One of these stars has a definite lithium detection and two other (fainter) stars have possible lithium detections. We find the lithium depletion boundary in IC2391 is at I_C=16.2, which implies an age for IC2391 of 53$pm$5 Myr. While this is considerably older than the age most commonly attributed for this cluster (~35 Myr), the correction factor to the IC2391 age is comparable to those recently derived for the Pleiades and alpha Per clusters and can be explained by new models for high mass stars that incorporate a modest amount of convective core overshooting.
rate research
Read More
We have obtained new photometry and intermediate resolution ($Delta lambda = 2.7$ AA ) spectra of 19 of these objects (14.9 $le$ $I_c$ $le$ 17.5) in order to confirm cluster membership. We identify 15 of our targets as likely cluster members based on their $VRI$ photometry, spectral types, radial velocity, and H$alpha$ emission strengths. Higher S/N spectra were obtained for 8 of these probable cluster members in order to measure the strength of the lithium 6708 AA doublet and thus obtain an estimate of the clusters age. One of these 8 stars has a definite lithium detection and two other (fainter) stars have possible lithium detections. A color-magnitude diagram for our program objects shows that the lithium depletion boundary in IC~2391 is at $I_c$=16.2. Using recent theoretical model predictions, we derive an age for IC~2391 of 53$pm$5 Myr. While this is considerably older than the age most commonly attributed for this cluster ($sim$35 Myr) this result for IC~2391 is comparable those recently derived for the Pleiades and Alpha Persei clusters and can be explained by new models for high mass stars that incorporate a modest amount of convective core overshooting.
High-dispersion spectra centered on the Li 6708 A line have been obtained for 70 potential members of the open cluster NGC 3680, with an emphasis on stars in the turnoff region. A measurable Li abundance has been derived for 53 stars, 39 of which have radial velocities and proper motions consistent with cluster membership. After being transferred to common temperature and abundance scales, previous Li estimates have been combined to generate a sample of 49 members, 40 of which bracket the cluster Li-dip. Spectroscopic elemental analysis of 8 giants and 5 turnoff stars produces [Fe/H] = -0.17 +/- 0.07 (sd) and -0.07 +/- 0.02 (sd), respectively. We also report measurements of Ca, Si and Ni which are consistent with scaled-solar ratios within the errors. Adopting [Fe/H] = -0.08 (Sect. 3.6), Y^2 isochrone comparisons lead to an age of 1.75 +/- 0.10 Gyr and an apparent modulus of (m-M) = 10.30 +/- 0.15 for the cluster, placing the center of the Li-dip at 1.35 +/- 0.03 solar masses. Among the giants, 5 of 9 cluster members are now known to have measurable Li with A(Li) near 1.0. A combined sample of dwarfs in the Hyades and Praesepe is used to delineate the Li-dip profile at 0.7 Gyr and [Fe/H] = +0.15, establishing its center at 1.42 +/- 0.02 solar masses and noting the possible existence of secondary dip on its red boundary. When evolved to the typical age of the clusters NGC 752, IC 4651 and NGC 3680, the Hyades/Praesepe Li-dip profile reproduces the observed morphology of the combined Li-dip within the CMDs of the intermediate-age clusters while implying a metallicity dependence for the central mass of the Li-dip given by Mass = (1.38 +/-0.04) + (0.4 +/- 0.2)[Fe/H]. The implications of the similarity of the Li-dichotomy among giants in NGC 752 and IC 4651 and the disagreement with the pattern among NGC 3680 giants are discussed.
It is unclear whether chemically peculiar stars of the upper main sequence represent a class completely distinct from normal A-type stars, or whether there exists a continuous transition from the normal to the most peculiar late F- to early B-type stars. A systematic abundance analysis of open cluster early-type stars would help to relate the observed differences of the chemical abundances of the photospheres to other stellar characteristics, without being concerned by possible different original chemical composition. Furthermore, if a continuous transition region from the very peculiar to the so called normal A-F stars exists, it should be possible to detect objects with mild peculiarities. As a first step of a larger project, an abundance analysis of 5 F-A type stars in the young cluster IC2391 was performed using high resolution spectra obtained with the UVES instrument of the ESO VLT. Our targets seem to follow a general abundance pattern: close to solar abundance of the light elements and iron peak elements, heavy elements are slightly overabundant with respect to the sun, similar to what was found in previous studies of normal field A-type stars of the galactic plane. We detected a weakly chemically peculiar star, HD74044. Its element pattern contains characteristics of CP1 as well as CP2 stars, enhanced abundances of iron peak elements and also higher abundances of Sc, Y, Ba and Ce. We did not detect a magnetic field in this star (detection limit was 2kG). We also studied the star SHJM2, proposed as a pre-main sequence object in previous works. Using spectroscopy we found a high surface gravity, which suggests that the star is very close to the ZAMS.
We review our the status of the photometric searches of brown dwarfs and vely low mass stars in several young open clusters and present some results on the spectroscopic follow-up, including new cluster ages based on the position of the lithium depletion boundary.
Galactic open clusters have been long recognized as one of the best tools to investigate the chemical content of Galactic disk and its time evolution. In the last decade, many efforts have been directed to chemically characterize the old and intermediate age population; surprisingly, the chemical content of the younger and close counterpart remains largely undetermined. In this paper we present the abundance analysis of a sample of 15 G/K members of the young pre-main sequence clusters IC 2602 and IC 2391. Along with IC 4665, these are the first pre-main sequence clusters for which a detailed abundance determination has been carried out so far. We analyzed high-resolution, high S/N spectra acquired with different instruments (UVES and CASPEC at ESO, and the echelle spectrograph at CTIO), using MOOG and equivalent width measurements. Along with metallicity ([Fe/H]), we measured NaI, SiI, CaI, TiI and TiII, and NiI abundances. Stars cooler than ~5500 show lower CaI, TiI, and NaI than warmer stars. By determining TiII abundances, we show that, at least for Ti, this effect is due to NLTE and over-ionization. We find average metallicities [Fe/H] =0$pm 0.01$ and [Fe/H]=0.01$pm$ 0.02 for IC 2602 and IC 2391, respectively. All the [X/Fe] ratios show a solar composition; the accurate measurements allow us to exclude the presence of star-to-star scatter among the members.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
