J/MNRAS/510/1894 Element abundances study of Cepheids (Kovtyukh+, 2022)
The MAGIC project - III. Radial and azimuthal Galactic abundance gradients
using classical Cepheids.
Kovtyukh V., Lemasle B., Bono G., Usenko I.A., Da Silva R., Kniazev A.,
Grebel E.K., Andronov I.L., Shakun L., Chinarova L.
<Mon. Not. R. Astron. Soc. 510, 1894-1901 (2022)>
=2022MNRAS.510.1894K 2022MNRAS.510.1894K (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, variable ; Models, atmosphere ; Optical ;
Spectroscopy ; Abundances ; Abundances, [Fe/H] ; Galactic center ;
Galactic plane ; Positional data ; Stars, distances ;
Effective temperatures
Keywords: stars: abundances - stars: variables: Cepheids
Abstract:
Radial abundance gradients provide sound constraints for
chemo-dynamical models of galaxies. Azimuthal variations of abundance
ratios are solid diagnostics to understand their chemical enrichment.
In this paper, we investigate azimuthal variations of abundances in
the Milky Way using Cepheids. We provide the detailed chemical
composition (25 elements) of 105 Classical Cepheids from high-
resolution SALT spectra observed by the MAGIC project. Negative
abundance gradients, with abundances decreasing from the inner to the
outer disc, have been reported both in the Milky Way and in external
galaxies, and our results are in full agreement with literature
results. We find azimuthal variations of the oxygen abundance [O/H].
While a large number of external spirals show negligible azimuthal
variations, the Milky Way seems to be one of the few galaxies with
noticeable [O/H] azimuthal asymmetries. They reach ≃0.2 dex in the
inner Galaxy and in the outer disc, where they are the largest, thus
supporting similar findings for nearby spiral galaxies, as well as
recent 2D chemo-dynamical models.
Description:
Radial abundance gradients provide sound constraints to galaxy
formation scenarios. Indeed, the star formation history, the accretion
history, the radial migration of stars, and the radial flows of gas
and their variations with the Galactocentric distance, simultaneously
determine the shape of abundance gradients. Chemo-dynamical models of
the Milky Way must therefore reproduce the observed gradients and
their evolution with time. We study those points from line elemetns
from powerfull spectrographs facilities.
In this paper, we present new results of the Milky WAy Galaxy wIth
SALT speCtroscopy project (MAGIC; Kniazev et al. 2019AstBu..74..208K 2019AstBu..74..208K),
a large spectroscopic survey that uses spectral instrumentation of the
Southern African Large Telescope (SALT; Buckley, Swart & Meiring
2006SPIE.6267E..0ZB; O'Donoghue et al. 2006MNRAS.372..151O 2006MNRAS.372..151O). MAGIC
targets pulsating variable stars, in particular, Cepheids in order to
study the Milky Way chemical evolution. We provide the stellar
parameters of 105 Classical Cepheids and the abundances of 25
elements, based on 122 high-resolution SALT spectra.
As evoked, we use spectroscopic data from the SALT HRS high-resolution
spectrograph providing two spectra in the blue and red arms over a
spectral range of ≃ 390-890 nm. More, the HRS primary data reduction,
including overscan and gain corrections, as well as bias subtractions,
was done through the SALT science pipeline (Crawford et al.
2010SPIE.7737E..25C 2010SPIE.7737E..25C). The spectroscopic reduction of the HRS data was
performed using our own HRS pipeline, described in detail in Kniazev
et al. 2016MNRAS.459.3068K 2016MNRAS.459.3068K and Kniazev et al. (2019AstBu..74..208K 2019AstBu..74..208K).
Observations informations and atmospheric data of our Milky Way
cepheids sample are exposed in the table1.dat (also see the section
2.2 Determination of abundances to have the atmosphere models LTE
approximation extrapoling all element abundances for specific
atmospheric parameters of each individual star). Hereafter, the
table3.dat and table4.dat detail all element abundances data from (C
to Mn and Fe to Gd element) for each cepheids, (all mean uncetainties
are provided in section 3.2 Radial abundance gradients).
Then as detailed in the section 3 (The galactic radial abundance
gradients and specifically the section 3.1 Distances), we study the
radial abundance gradient with help of computed galacto/heliocentric
distances, azimuthal angles (from galactic positions) and cepheids
periods of our stars. All these values are available in the
table2.dat. As conclusion, we report the chemical composition (25
elements) of 105 classical Cepheids. Abundances have been derived from
122 high-resolution SALT spectra observed in the context of the MAGIC
project, (i.e see section Conclusion and section 2 Spectroscopic
analysis).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 85 116 Spectra informations and atmospheric parameters
for the investigated Cepheids
table2.dat 66 105 Helio/Galactocentric distribution of our 105
cepheids sample
table3.dat 97 104 *Abundances from C to Mn of our cepheids sample
table4.dat 85 104 *Abundances from Fe to Gd of our cepheids sample
--------------------------------------------------------------------------------
Note on table3.dat and table4.dat: The abundances are expressed on the common
astronomical logarithmic abundance scale. Hydrogen is the natural reference
element for solar (and stellar) spectroscopy, both because it is the most
abundant element and because it provides the continuous opacity in the optical
and infrared through the negative hydrogen ion H-. The normalisation of the
elemental number density NX for an element X is defined as
log EX = log(NX/NH) + 12.00, for historical reasons, hence
log EH = 12.00 (i.e refer to Asplund et al. 2021A&A...653A.141A 2021A&A...653A.141A).
In our study, we derived abundances with LTE approximation using atmosphere
models interpolated for the specific atmospheric parameters of each individual
star within the grid of models by Castelli & Kurucz 2003IAUS..210P.A20C
(i.e refer to section 2.2 Determination of abundances).
--------------------------------------------------------------------------------
See also:
J/A+A/381/32 : Galactic Cepheid abundances (Andrievsky+, 2002)
J/AJ/156/171 : Cepheid abund.: multiphase results & spatial gradients
(Luck, 2018)
J/A+A/616/A82 : Physical parameters of classical Cepheids (Proxauf+, 2018)
J/ApJ/885/131 : ∼200 high-mass SFR plx & proper motion with VLBI (Reid+, 2019)
J/AcA/69/305 : Northern Galactic disk classical Cepheids (Skowron+, 2019)
J/ApJ/852/78 : JHKs, WISE and Spitzer data of Galactic Cepheids (Wang+, 2018)
https://astronomers.salt.ac.za/ : SALT data home page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Object Object cepheid name (Object)
15- 24 F10.5 d MJD Modified Julian Date (MJD-2450000)
26- 29 I4 s ExpTime Exposure time (Exptime)
31- 34 I4 K Teff Effective temperature (Teff) (1)
36- 38 I3 K e_Teff Mean 1 σ Teff uncertainty (σ)
40- 41 I2 --- o_Teff The number N of line depth ratios used
to derive Teff (N)
43- 46 F4.1 K SETeff ? Standard error of the mean value Teff
computed as σ/sqrt(N) (σ/sqrtN)
48- 51 F4.2 [cm/s2] log(g) ? Logarithm of surface gravity (logg) (2)
53- 56 F4.2 km/s Vt ? Microturbulence velocity (Vt) (2)
58- 62 F5.2 [Sun] [Fe/H] ? Abundance [Fe/H] in solar units ([Fe/H]) (3)
64- 67 F4.2 [Sun] e_[Fe/H] ? Mean 1 σ [Fe/H] uncertainty (Sigma)
69- 71 I3 --- o_[Fe/H] ? The number N of Fe I lines used
to derive [Fe/H] (n)
73- 85 A13 --- Remarks Additional remarks (Remarks)
--------------------------------------------------------------------------------
Note (1): As explained in the section 2.2 Determination of abundances, Teff
was derived from line-depth ratios (Kovtyukh 2007MNRAS.378..617K 2007MNRAS.378..617K),
a technique commonly employed in studies of Cepheid variables (e.g.
Andrievsky et al. 2002A&A...381...32A 2002A&A...381...32A, Cat. J/A+A/381/32; Lemasle et
al. 2007A&A...467..283L 2007A&A...467..283L; Luck 2018AJ....156..171L 2018AJ....156..171L, Cat. J/AJ/156/171;
Proxauf et al. 2018A&A...616A..82P 2018A&A...616A..82P, Cat. J/A+A/616/A82).
Note (2): Once Teff determined, the surface gravity log g was computed by
imposing the iron ionization balance. The microturbulent velocity,
Vt, was derived assuming that there is no correlation between the
iron abundance A(Fe), obtained from Fe I lines, and the equivalent
widths (EW) of the same lines, (see section 2.2 Determination of
abundances).
Note (3): The adopted value for [Fe/H] is the one derived from the Fe I lines,
since we imposed the ionization balance and because they outnumber
Fe II lines, (see section 2.2 Determination of abundances).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Object Object cepheid name (Object)
16- 21 F6.2 deg GLON Galactic longitude (l) (1)
23- 27 F5.2 deg GLAT Galactic latitude (b) (1)
29- 33 I5 pc D Heliocentric distance (Distance) (1)
35- 44 F10.7 d P Pulsation mode period (Period) (1)
46- 47 A2 --- Mode [F 1O] Pulsation mode (Mode) (2)
49- 54 F6.2 deg phi The cepheid azimuthal angle φ (φ) (3)
56- 60 F5.2 kpc Rg Galactocentric distances (Rg) (1)
62- 66 F5.2 [Sun] [Fe/H] Abundance [Fe/H] in solar units ([Fe/H]) (4)
--------------------------------------------------------------------------------
Note (1): For our new sample, as well as for the Cepheids from the literature,
we have computed the Galactocentric distances by adopting a distance
to the Galactic centre of RG,☉= 8.15 kpc (Gravity Collaboration
2019A&A...625L..10G 2019A&A...625L..10G; Reid et al. 2019ApJ...885..131R 2019ApJ...885..131R,
Cat. J/ApJ/885/131) and heliocentric distances to Cepheids from
Skowron et al. (2019AcA....69..305S 2019AcA....69..305S, Cat. J/AcA/69/305).
Skowron et al. (2019AcA....69..305S 2019AcA....69..305S, Cat. J/AcA/69/305) used
mid-infrared Spitzer (Churchwell et al. 2009PASP..121..213C 2009PASP..121..213C) and WISE
(Mainzer et al. 2011ApJ...731...53M 2011ApJ...731...53M) photometry together with the
mid-infrared period-luminosity relations derived by Wang et al.
(2018ApJ...852...78W 2018ApJ...852...78W, Cat. J/ApJ/852/78) and the extinction maps of
Bovy et al. (2016ApJ...818..130B 2016ApJ...818..130B).
Note (2): We denoted two different cepheid pulsation modes as follows:
F = Fundamental frequency pulsating mode
1O = First overtone cepheid frequency pulsating mode
Note (3): As explained in the section 3.3 The azimuthal abundance gradient, the
azimuth φ is defined as the angle between the Galactocentric
radius containing a given Cepheid and the reference radius (φ=0)
containing both the Sun and the Galactic centre. φ increases with
the Galactocentric longitude.
Note (4): The adopted value for [Fe/H] is the one derived from the Fe I lines,
since we imposed the ionization balance and because they outnumber
Fe II lines, (see section 2.2 Determination of abundances).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Object Object cepheid name (Object)
15- 19 F5.2 [-] [C/H] ? Carbon abundance
21- 25 F5.2 [-] [N/H] ? Nitrogen abundance
27- 31 F5.2 [-] [O/H] ? Oxygen abundance
33- 37 F5.2 [-] [Na/H] ? Sodium abundance
39- 43 F5.2 [-] [Mg/H] ? Magnesium abundance
45- 49 F5.2 [-] [Al/H] ? Aluminium abundance
51- 55 F5.2 [-] [Si/H] ? Silicon abundance
57- 61 F5.2 [-] [S/H] ? Sulfur abundance
63- 67 F5.2 [-] [Ca/H] ? Calcium abundance
69- 73 F5.2 [-] [Sc/H] ? Scandium abundance
75- 79 F5.2 [-] [Ti/H] ? Titanium abundance
81- 85 F5.2 [-] [V/H] ? Vanadium abundance
87- 91 F5.2 [-] [Cr/H] ? Chromium abundance
93- 97 F5.2 [-] [Mn/H] ? Manganese abundance
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Object Object cepheid name (Object)
15- 19 F5.2 [-] [Fe/H] ? Iron abundance
21- 25 F5.2 [-] [Co/H] ? Cobalt abundance
27- 31 F5.2 [-] [Ni/H] ? Nichel abundance
33- 37 F5.2 [-] [Y/H] ? Yttrium abundance
39- 43 F5.2 [-] [Zr/H] ? Zirconium abundance
45- 49 F5.2 [-] [La/H] ? Lanthanum abundance
51- 55 F5.2 [-] [Ce/H] ? Cerium abundance
57- 61 F5.2 [-] [Pr/H] ? Praseodymium abundance
63- 67 F5.2 [-] [Nd/H] ? Neodymium abundance
69- 73 F5.2 [-] [Sm/H] ? Samarium abundance
75- 79 F5.2 [-] [Eu/H] ? Europium abundance
81- 85 F5.2 [-] [Gd/H] ? Gadolinium abundance
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 23-Oct-2024