J/MNRAS/499/2701 λ Bootis stars: the Southern Survey II. (Murphy+, 2020)
The discovery of lambda Bootis stars - the Southern Survey II.
Murphy S.J., Gray R.O., Corbally C.J., Kuehn C., Bedding T.R., Killam J.
<Mon. Not. R. Astron. Soc., 499, 2701-2713 (2020)>
=2020MNRAS.499.2701M 2020MNRAS.499.2701M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, peculiar ; Stars, early-type ; Stars, emission ;
Spectral types ; Effective temperatures ; Abundances ;
Reddening ; Spectra, optical ; Infrared
Keywords: stars: chemically peculiar - circumstellar matter -
stars: early-type - stars: emission-line, Be - stars: evolution
Abstract:
The λ Boo stars are chemically peculiar A-type stars whose
abundance anomalies are associated with the accretion of metal-poor
material. We searched for λ Boo stars in the Southern
hemisphere in a targeted spectroscopic survey of metal-weak and
emission-line stars. Obtaining spectra for 308 stars and classifying
them on the MK system, we found or co-discovered 24 new λ Boo
stars. We also revised the classifications of 11 known λ Boo
stars, one of which turned out to be a chemically normal rapid
rotator. We show that stars previously classified in the literature as
blue horizontal branch stars or emission-line A stars have a high
probability of being λ Boo stars, although this conclusion is
based on small-number statistics. Using WISE infrared fluxes, we
searched our targets for infrared excesses that might be attributable
to protoplanetary or debris discs as the source of the accreted
material. Of the 34 λ Boo stars in our sample, 21 at various
main-sequence ages have infrared excesses, confirming that not all
λ Boo stars are young.
Description:
To improve the success rate of searching for λ Boo stars beyond
the 2 per cent one expects at random, we compiled a target list from
several types of stars that we considered likely to yield new λ
Boo stars. A major focus in this work was emission-line A stars, but
relatively few (<50) of these are known. Blue horizontal branch (BHB)
stars are another class of rare metal-weak A stars that we considered
to be promising targets. The target list therefore contained a mixture
of emission-line stars, BHB stars, and a large number of metal-poor
stars selected using Stromgren photometry. Due to good weather and
efficient observing, we added a further group of targets on the final
night of the observing run, comprising A and early F stars observed in
Campaign 01 of the K2 Mission.
During 2014 March 17-19, we obtained spectra of 308 targets with the
WiFeS spectrograph (Dopita et al. 2007Ap&SS.310..255D 2007Ap&SS.310..255D) on the ANU
2.3-m telescope at Siding Spring Observatory. Our spectra were
obtained in the blue-violet region in B3000 mode and have a resolution
of about 2.5Å/2 pixels. The WiFeS data were reduced with the
PYWIFES software package (Childress et al. 2014Ap&SS.349..617C 2014Ap&SS.349..617C). Due
to difficulty in rectifying the spectra over the Balmer jump, we
trimmed the spectra to the range 3865-4960Å. The spectra thus cover
the region between the blue wing of H8 and the red wing of Hβ.
The spectra are qualitatively similar to those made from SAAO for
Paper I (Gray et al., 2017AJ....154...31G 2017AJ....154...31G, Cat. J/AJ/154/31).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 115 157 Infrared excesses for all stars of the sample
with a ≥2σ excess in one or more WISE
bands
table3.dat 64 151 Parameters from SED fitting, for the stars
without detected infrared excesses
tablea1.dat 372 309 Spectral classes for the program stars
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See also:
J/AJ/154/31 : λ Bootis stars: the southern survey I. (Gray+, 2017)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name Star name
13- 41 A29 --- SpType Spectral type
43 I1 --- Boo [0/1] Indicates whether the star is in the
lambda Boo class (1:yes; 0:no)
45 A1 --- Norm Normalisation band (Johnson V or 2MASS J)
47- 51 I5 K Teff Effective temperature
53- 55 F3.1 [cm/s2] logg Logarithm of the surface gravity
57- 60 F4.1 [-] [Fe/H] Fe/H abundance ratio
62- 66 F5.3 mag E(B-V) ? Reddening E(B-V)
68- 72 F5.1 --- fW1 ? Flux fraction in excess of the model in the
W1 band (1)
74- 77 F4.1 --- e_fW1 ? Error on fW1
79- 83 F5.1 --- fW2 ? Flux fraction in excess of the model in the
W2 band (1)
85- 88 F4.1 --- e_fW2 ? Error on fW2
90- 95 F6.1 --- fW3 ? Flux fraction in excess of the model in the
W3 band (1)
97- 101 F5.1 --- e_fW3 ? Error on fW3
103- 109 F7.1 --- fW4 ? Flux fraction in excess of the model in the
W4 band (1)
111- 115 F5.1 --- e_fW4 ? Error on fW4
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Note (1): Infrared excesses are given as the flux fraction in excess of the
model, i.e. (Fobs-Fmodel)/Fmodel
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name Star name
13- 39 A27 --- SpType Spectral type
41 I1 --- Boo [0/1] Indicates whether the star is in the
lambda Boo class (1:yes; 0:no)
43 A1 --- Norm Normalisation band (Johnson V or 2MASS J)
45- 49 I5 K Teff ? Effective temperature
51- 53 F3.1 [cm/s2] logg ? Logarithm of the surface gravity
55- 58 F4.1 [-] [Fe/H] ? Fe/H abundance ratio
60- 64 F5.3 mag E(B-V) ? Reddening E(B-V)
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Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name Star name
13- 17 F5.2 mag Vmag ? V-band magnitude
19- 20 A2 --- Group Target group (1)
22- 52 A31 --- SpType Spectral type
54- 370 A317 --- Com Comment on the spectrum of the star
372 I1 --- IR [0/1] Indicates if the star has an infrared
excess (1:yes; 0:no)
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Note (1): Targets were organized into groups based on how they were selected.
See section 2.1 for more details. Group as follows:
0 = Known λ Boo star (11/309)
1 = Emission-line A star (i). We used the criteria search function of the
SIMBAD data base (Wenger et al. 2000A&AS..143....9W 2000A&AS..143....9W) to select spectral
types matching 'A[0-9]*e', where '[0-9]' represents any integer in this
range, the asterisk is a wildcard of any length, and 'e' is the standard
notation for emission lines (20/309)
2 = Emission-line A star (ii). This group is phenomenologically identical
to the previous group, except that the search terms were slightly
modified to capture stars whose spectral types had been recorded
differently. We searched for object types matching 'Em*/Ae*' and
'spectral type=A' (18/309)
3 = Photometrically metal-weak star (211/309)
4 = Blue horizontal branch (BHB) star (7/309)
K2 = Target scheduled to be observed in Campaign 01 of the K2 Mission
(42/309)
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History:
From electronic version of the journal
References:
Gray et al., Paper I 2017AJ....154...31G 2017AJ....154...31G, Cat. J/AJ/154/31
(End) Ana Fiallos [CDS] 05-Sep-2023