J/A+A/687/A118 VELOCE modulation zoo. I. (Netzel+, 2024)
The VELOCE modulation zoo. I. Spectroscopic detection of non-radial modes in the
first-overtone Cepheids BG Crucis, QZ Normae, V0391 Normae, and V0411 Lacertae.
Netzel H., Anderson R.I., Viviani G.
<Astron. Astrophys. 687, A118 (2024)>
=2024A&A...687A.118N 2024A&A...687A.118N (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Radial velocities ; Optical
Keywords: techniques: radial velocities - stars: oscillations -
stars: variables: Cepheids
Abstract:
The photometric observations from the recent decade revolutionized our
view on classical pulsators. Low-amplitude signals have been detected
photometrically in addition to the dominant high-amplitude radial mode
pulsations in many RR Lyrae stars and classical Cepheids. First
overtone pulsators with an additional low-amplitude signal at a period
ratio of around 0.61 with the main mode, the so-called 0.61 stars,
form the most populous group among these stars. The nature of this
signal has been attributed to non-radial pulsations. Another
mysterious group are stars, where the additional signal forms a period
ratio of around 0.68. These are the 0.68 stars. The origin of the
signal remains unknown.
Here, we search for similar phenomena in spectroscopic observations of
first-overtone classical Cepheids collected as part of the VELOCE
project.
We performed frequency analysis of several parameters derived from
cross-correlation functions (CCFs), including radial velocity (RV),
full width at half maximum (FWHM), bisector inverse span (BIS), and
CCF depth (contrast). Using standard prewhitening, we searched for
additional low-amplitude signals. We identify the location of these
stars in various sequences of the Petersen diagram.
We detect additional signals in four first-overtone classical
Cepheids: BG Cru, QZ Nor, V0391 Nor, and V0411 Lac. We classified
BG Cru, QZ Nor, and V0391 Nor as 0.61 stars based on period ratios.
V0411 Lac, however, exhibits a ratio of 0.68 between the two modes,
and the additional signal has a longer period. This kind of
multiperiodicity remains unexplained.
VELOCE CCFs yield the first spectroscopic detections of non-radial
pulsation modes in classical Cepheids. This opens an asteroseismic
window for pursuing a more detailed understanding of these important
stars. While the 0.61 signal of BG Cru, QZ Nor, V0391 Nor is
understood to originate due to non-radial modes of moderate degrees,
the 0.68 signal of V0411 Lac still lacks a physical explanation.
Description:
The VELOCE project has collected high-resolution spectroscopic
time-series observations with baselines exceeding a decade of an
unprecedented number of Cepheids from both hemispheres. The details of
the data collection for the VELOCE project can be found in VELOCE-I
(Anderson et al., 2014A&A...566L..10A 2014A&A...566L..10A, Cat. J/A+A/566/L10).
Analyzed RV, FWHM, BIS, and contrast data for BG Cru, QZ Nor,
V0391 Nor, and V0411 Lac are collected in table 2.
Objects:
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RA (2000) DE Designation(s)
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12 31 40.33 -59 25 26.1 BG Cru = HD 108968
16 11 20.46 -54 21 14.8 QZ Nor = HD 144972
15 31 52.59 -59 14 59.2 V0391 Nor = HD 137941
22 28 58.32 +50 57 47.2 V0411 Lac = HD 213233
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 4 Summary of the data for the four stars
table2.dat 67 838 Analyzed data
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See also:
J/A+A/566/L10 : Cepheid radial velocity amplitude modulations (Anderson, 2014)
J/A+A/686/A177 : VELOCE I. Cepheids High-precision RVs (Anderson+, 2024)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star name
11- 12 I2 h RAh Simbad right ascension (J2000)
14- 15 I2 min RAm Simbad right ascension (J2000)
17- 21 F5.2 s RAs Simbad right ascension (J2000)
23 A1 --- DE- Simbad declination sign (J2000)
24- 25 I2 deg DEd Simbad declination (J2000)
27- 28 I2 arcmin DEm Simbad declination (J2000)
30- 33 F4.1 arcsec DEs Simbad declination (J2000)
35- 41 A7 --- Inst Instrument
43- 49 I7 d BJD1 Lower value of BJD range
50 A1 --- --- [-]
51- 57 I7 d BJD2 Upper value of BJD range
59- 61 I3 --- <S/N> Average S/N of the CCF profiles calculated
using the tool FAMIAS (Zima, 2008,
Communications in Asteroseismology, 157, 387)
63- 65 I3 --- Nobs Number of observations
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star name
11- 21 F11.5 d BJD Barycentric Julian date (BJD-2400000)
23- 31 F9.5 km/s RV Radial velocity
33- 37 F5.3 km/s e_RV Radial velocity error
40- 47 F8.5 km/s FWHM Full width at half maximum
50- 57 F8.5 km/s BIS Bisector inverse span
60- 67 F8.5 --- Contrast Relative depth
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Acknowledgements:
Henryka Netzel, henia(at)netzel.pl
(End) Patricia Vannier [CDS] 20-Jun-2024