Arqueología galáctica: Detectando estrellas fósiles en la Vía Láctea

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1 Arqueología galáctica: Detectando estrellas fósiles en la Vía Láctea ANDRÉS MEZA U N I V E R S I D A D A U TÓ N O M A D E C H I L E FA C U LTA D D E I N G E N I E R Í A M I E M B R O L S S T, C L U E S Y A G O R A

2 Características de la Vía Láctea La Vía Láctea es una galaxia espiral barrada con un disco de 30 kpc de diámetro, un núcleo con una barra de 4 kpc y una halo estelar extendido. Posee una masa de aprox. 10 #$ M con una masa estelar de 5 10 #* M. El Sol se ubica a 8 kpc del centro. NGC3953 1

3 proyección XY sólo estrellas color = edad proyección XZ Abadi et al. ApJ, 591, 499 (2003) 2

4 Formación de galaxias Las estrellas son depositadas tanto en el halo como el en disco de la galaxia principal. Satélites en órbitas coplanares con el disco depositan sus estrellas en él. Mientras que los satélites en órbitas casi polares dispersan sus estrellas en el halo de la galaxia principal. 40 kpc Meza et al. MNRAS, 93, 105 (2005) 3

5 Detectando estrellas peculiares en la Vía Láctea M/H = log N 3 log N 3 N N 4 5:; Majewski et al. AJ, 154, 94 (2017) Apogee-2 Survey 4

6 icorrelation for the three different metallicity groups present in ω Centauri (magenta stars). For each metallicity bin, the stars in our sample were The Kapteyn group has stars in the metal-poor and metal-intermediate groups. In the middle and right panels the two GC second-generation field írez et al. (2012) are also plotted, as solid yellow stars. Grupo de Kapteyn Fernández-Trincado et al. ApJ, 846, L2 (2017) Journal, (7pp), 2016for December Figure 1. Abundance ratios in three different planes: (a) [Mg/Fe] [Al/Fe],The (b) Astrophysical [Fe/H] [Mg/Fe], and (c)833:132 [N/Fe] [Al/Fe], the new20field SG GC-like stars (red star symbols for DR13 abundances, orange circles for our manual analysis) overlaid with MW field stars, N-rich halo stars (Martell et al. 2016), N-rich bulge stars (Schiavon et al. 2017b), and FG and SG populations in GCs M2, M3, M5, M107, M71, and M13 (Mészáros et al. 2015). Open circles indicate the SG-like candidates with [Fe/H] < 1. In (a) the gray dashed line marks the loci of the SG GC-like candidates, above [Al/Fe] > +0.1 ([Mg/Fe] < +0.18) and [Al/Fe] > based on k-means m and aluminum abundances for our target([mg/fe] > +0.18), stars (same symbols as in Figure 3). Onlyclustering. 3 of the 14 stars observed from the Kapteyn group have es measured. Magenta starred symbols are GC stars from the catalog of Carretta et al. (2009a), which show a broad Mg Al anticorrelation. Gray halo and disk stars from Chen et al. (2000) and Reddy et al. (2003, 2006). Fernández-Trincado et al. Navarrete et al. ApJ, 807, 103 (2015) code Turbospectrum (Alvarez & Plez 1998) and MARCS model atmospheres (Gustafsson et al. 2008). In particular, a mix of abundances. Examples for a portion of the observed APOGEE spectra (spectral region covering CN, Mg, and Al lines) are shown e consistent with their He I EWs, assuming the Given that the He I Å line is associated with activity in heavily and stars, α-poor models were used.among The a few in of Figure icative of helium content. For red giantscn-cycle in cool wemarcs also explore its variability the 2 for our 11 anomalous stars. Table 1 lists the final set of same molecular lines by Smith et al. and Souto parameters and chemical abundances for each star GC with no significant helium enhancement stars adopted in our samples using our(2013) own data obtained foratmospheric another et al.several (2016) were employed to determine C, N, and available O obtained 0.04), Smith et al. (2014) found program, as well as some the measurements in the through ASPCAP DR13 (first line) and the line-by-line lower than 40 må, similar to the distribution literature. CRIRES spectra were obtained for HD 13979, HD apteyn and ω Cen groups , and HD about a year after the observations 3 ontrol sample of field stars, HD and HD reported in the present work. Using the same reduction process, deviate from all the stars in all of our samples. the spectrum around Å was extracted, and in Figure 8 we s an EW of the order of magnitude of those show the normalized spectra at the two epochs for the three cool stars (see Sanz-Forcada & Dupree 2008), stars. Both HD and HD show an indistinguishstudies reported a measurement for the helium able helium line shape between the two observations. In r. HD has a He I EW about 5 6 times contrast, the He I line in HD changes from being not maximum distance Z max from the Galactic plane as a function of the orbital eccentricity for 2M and 63 GC from Moreno et al. verage value for the remaining stars in our field detected on the first run (EW smaller than 10Figure må) 4.toLeft: appearing (2014). The open star symbol refers to NGC The horizontal black dashed line represents 3 kpc, the higher limit for the thick disc proposed by Carollo et al. reover, it has an enhanced [Ba/Fe] abundance in emission a year later, with an EW of 50 må. (2010). Right: meridional orbit of 2M computed with Model 3 (black line) and Model 4 (red dashed line). Finally, we found differences in the He I EW measurements makes it an intriguing target in its own right in the literature for two stars in our ω Cen group (see Table 7). ). since this star shows nitrogen enhancement similar to A more exotic explanation of such peculiar chemistry in 5 a that of Schiavon s sample, i.e., 2M , disk-like orbit star is that it could be chemically linked with the 13 like the N-rich population, has elevated nitrogen abundance, 2M Fernández-Trincado et al. ApJ, 833, 132 (2016) [N/Fe] = 1.46 dex (see Table 1). Interestingly, our orbital solutions show that 2M passes through the Galactic bulge at its closest approach to the Galactic center Rmin 0.62 kpc and reaches a maximum distance from the Galactic center at Rmax < 7.26 kpc (see the orbit projection in Figure 4) in an eccentric orbit e = Given its peculiar chemical fingerprint and orbital elements within the Galactic disk, this star could be interpreted as a N-rich bulge interloper. It is interesting to note that there are a handful of N-rich stars from Schiavon s sample with intermediate Al abundance and ω Cen progenitor system, from which it might have been ejected. However, ω Cen is a very complex and unusual stellar system in the Milky Way, and its origin is still not well understood (GC or dsph galaxy?). Other GC progenitor candidates might be examined with more detail in the near future, given the upcoming and more accurate six-dimensional phase-space data set that will be produced by the Gaia space mission. The authors wish to thank the referee for their constructive

7 El cielo es el límite Gaia DR1 DR2 -> abril 2018: Posiciones, paralajes y movimientos propios para más de 109 objetos Gaia Collaboration. A&A, 595, A2 (2016) 6

8 El cielo es el límite SDSS-V: Pioneering Panoptic Spectroscopy. 4. Stellar astrophysical targets in the MWM: The J K color and absolute J magnitude of 0.00 Kollmeir et al. arxiv: (2017) 7