J/A+A/648/A78 Orphan stream RR Lyrae and non-variables (Prudil+, 2021) Milky Way archaeology using RR Lyrae and type II Cepheids. I. The Orphan stream in 7D using RR Lyrae stars. Prudil Z., Hanke M., Lemasle B., Crestani J., Braga V.F., Fabrizio M., Koch-Hansen A. J., Bono G., Grebel E.K., Matsunaga N., Marengo M., da Silva R., Dall'Ora M., Martinez-Vazquez C.E., Altavilla G., Lala H., Chaboyer B., Ferraro I., Fiorentino G., Gilligan C. Nonino M., Thevenin F. =2021A&A...648A..78P 2021A&A...648A..78P (SIMBAD/NED BibCode) ADC_Keywords: Milky Way ; Stars, variable ; Stars, distances ; Radial velocities Keywords: Galaxy: halo - Galaxy: kinematics and dynamics - Galaxy: structure - stars: variables: RR Lyrae Abstract: We present a chemo-dynamical study of the Orphan stellar stream using a catalog of RR Lyrae pulsating variable stars for which photometric, astrometric, and spectroscopic data are available. Employing low-resolution spectra from the Sloan Digital Sky Survey (SDSS), we determined line-of-sight velocities for individual exposures and derived the systemic velocities of the RR Lyrae stars. In combination with the stars' spectroscopic metallicities and Gaia EDR3 astrometry, we investigated the northern part of the Orphan stream. In our probabilistic approach, we found 20 single mode RR Lyrae variables likely associated with the Orphan stream based on their positions, proper motions, and distances. The acquired sample permitted us to expand our search to nonvariable stars in the SDSS dataset, utilizing line-of-sight velocities determined by the SDSS. We found 54 additional nonvariable stars linked to the Orphan stream. The metallicity distribution for the identified red giant branch stars and blue horizontal branch stars is, on average, -2.13±0.05dex and -1.87±0.14dex, with dispersions of 0.23 and 0.43dex, respectively. The metallicity distribution of the RR Lyrae variables peaks at -1.80±0.06dex and a dispersion of 0.25dex. Using the collected stellar sample, we investigated a possible link between the ultra-faint dwarf galaxy Grus II and the Orphan stream. Based on their kinematics, we found that both the stream RR Lyrae and Grus II are on a prograde orbit with similar orbital properties, although the large uncertainties on the dynamical properties render an unambiguous claim of connection difficult. At the same time, the chemical analysis strongly weakens the connection between both. We argue that Grus II in combination with the Orphan stream would have to exhibit a strong inverse metallicity gradient, which to date has not been detected in any Local Group system. Description: In our investigation, we identified 20 RR Lyrae variables (13 RRab and 7 RRc-type pulsators) to be associated with the Orphan stream based on their equatorial coordinates, proper motions, and distances, listed in table D1. We recovered 54 nonvariable stars likely associated with the Orphan stream as traced by our sample of RR Lyrae variables (listed in Table D.2). File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tabled1.dat 240 20 RR Lyrae stars in Orphan stream tabled2.dat 212 54 Non variable stars in Orphan stream -------------------------------------------------------------------------------- See also: I/350 : Gaia Early Data Release 3 (Gaia EDR3) (Lindegren+ 2020) V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015) J/AJ/136/2050 : SEGUE stellar parameter pipeline. II. (Lee+, 2008) J/AJ/153/204 : RR Lyrae stars from the PS1 3π survey (Sesar+, 2017) J/ApJ/765/154 : RR Lyrae stars in the Catalina Sky Survey (Drake+, 2013) Byte-by-byte Description of file: tabled1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 19 I19 --- ObjID SDSS source ID 20 A1 --- n_ObjID [*] * for star not used as reference sample in Sect. 4.2 22- 40 I19 --- GaiaEDR3 Gaia EDR3 source ID 42- 59 F18.14 deg RAdeg Right ascension (J2000) 61- 78 F18.15 deg DEdeg Declination (J2000) 80- 97 F18.12 pc d Distance 99-116 F18.13 pc e_d Uncertainty on distance 118-135 F18.14 km/s Vsys Systemic velocity 137-155 F19.16 km/s e_Vsys Uncertainty on systemic velocity 157-165 F9.6 mag VCSS Mean V band magnitude (Catalina photometry) 167-174 F8.6 mag e_VCSS Uncertainty on mean V band magnitude 176-183 F8.6 d P Pulsation period 185-196 F12.6 d M0 Time of brightness maxima 198-205 F8.6 mag AmpVCSS Pulsation amplitude (Catalina photometry) 207-210 A4 --- Type Pulsation RR Lyrae type 212-216 F5.2 [-] [Fe/H] Metallicity 218-236 F19.17 --- P(A/B) The conditional prob. of membership 238-240 A3 --- Note [K19 -] Known from Koposov et al. (2019MNRAS.485.4726K 2019MNRAS.485.4726K) -------------------------------------------------------------------------------- Byte-by-byte Description of file: tabled2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 19 I19 --- ObjID SDSS source ID 21- 39 I19 --- GaiaEDR3 Gaia EDR3 source ID 41- 58 F18.14 deg RAdeg Right ascension (J2000) 60- 77 F18.15 deg DEdeg Declination (J2000) 79- 88 F10.6 km/s RV Adopted radial velocity 90- 99 F10.7 km/s e_RV Uncertainty on adopted radial velocity 101-109 F9.6 mag gmag g-band magnitude 111-125 F15.9 mag e_gmag ?=-9999 Uncertainty on g-band magnitude 127-135 F9.4 K Teff Adopted Effective temperature 137-146 F10.6 K e_Teff Uncertainty on adopted effective temperature 148-157 F10.7 --- [Fe/H] Adopted Metallicity 159-169 F11.9 --- e_[Fe/H] Uncertainty on adopted metallicity 171-180 F10.8 --- logg Adopted Surface gravity 182-192 F11.9 --- e_logg Uncertainty on adopted surface gravity 194-212 F19.17 --- P(A/B) The conditional probability of membership -------------------------------------------------------------------------------- Acknowledgements: Zdenek Prudil, prudilz(at)ari.uni-heidelberg.de (End) Zdenek Prudil [ARI, Germany], Patricia Vannier [CDS] 21-Apr-2021