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See detailThe PLATO Simulator: modelling of high-precision high-cadence space-based imaging
Marcos-Arenal, P.; Zima, W.; De Ridder, J. et al

in Astronomy and Astrophysics (2014)

Many aspects of the design trade-off of a space-based instrument and its performance can best be tackled through simulations of the expected observations. The complex interplay of various noise sources in ... [more ▼]

Many aspects of the design trade-off of a space-based instrument and its performance can best be tackled through simulations of the expected observations. The complex interplay of various noise sources in the course of the observations make such simulations an indispensable part of the assessment and design study of any space-based mission. We present a formalism to model and simulate photometric time series of CCD images by including models of the CCD and its electronics, the telescope optics, the stellar field, the jitter movements of the spacecraft, and all important natural noise sources. This formalism has been implemented in a versatile end-to-end simulation software tool, called PLATO Simulator, specifically designed for the PLATO space mission to be operated from L2, but easily adaptable to similar types of missions. We provide a detailed description of several noise sources and discuss their properties, in connection with the optical design, the allowable level of jitter, the quantum efficiency of the detectors, etc. The expected overall noise budget of generated light curves is computed as a function of the stellar magnitude, for different sets of input parameters describing the instrument properties. The simulator is offered to the scientific community for future use. [less ▲]

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See detailGravito-inertial and pressure modes detected in the B3 IV CoRoT target HD 43317
Pápics, P. I.; Briquet, Maryline ULg; Baglin, A. et al

in Astronomy and Astrophysics (2012), 542

Context. OB stars are important building blocks of the Universe, but we have only a limited sample of them well understood enough from an asteroseismological point of view to provide feedback on the ... [more ▼]

Context. OB stars are important building blocks of the Universe, but we have only a limited sample of them well understood enough from an asteroseismological point of view to provide feedback on the current evolutionary models. Our study adds one special case to this sample, with more observational constraints than for most of these stars. <BR /> Aims: Our goal is to analyse and interpret the pulsational behaviour of the B3 IV star HD 43317 using the CoRoT light curve along with the ground-based spectroscopy gathered by the HARPS instrument. This way we continue our efforts to map the β Cep and SPB instability strips. <BR /> Methods: We used different techniques to reveal the abundances and fundamental stellar parameters from the newly-obtained high-resolution spectra. We used various time-series analysis tools to explore the nature of variations present in the light curve. We calculated the moments and used the pixel-by-pixel method to look for line profile variations in the high-resolution spectra. <BR /> Results: We find that HD 43317 is a single fast rotator (v[SUB]rot[/SUB] ≈ 50% v[SUB]crit[/SUB]) and hybrid SPB/β Cep-type pulsator with Solar metal abundances. We interpret the variations in photometry and spectroscopy as a result of rotational modulation connected to surface inhomogeneities, combined with the presence of both g and p mode pulsations. We detect a series of ten consecutive frequencies with an almost constant period spacing of 6339 s as well as a second shorter sequence consisting of seven frequencies with a spacing of 6380 s. The dominant frequencies fall in the regime of gravito-inertial modes. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Based on data gathered with HARPS installed on the 3.6 m ESO telescope (ESO Large Programme 182.D-0356) at La Silla, Chile.Table A.1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A55">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A55</A> [less ▲]

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See detailFirst evidence of pulsations in Vega?. Results of today's most extensive spectroscopic search
Böhm, T.; Lignières, F.; Wade, G. et al

in Astronomy and Astrophysics (2012), 537

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown ... [more ▼]

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown that it is a rapid rotator seen nearly pole one, a rare orientation particularly interesting for seismic studies. In this paper, we present a first systematic search for pulsations in Vega. <BR /> Aims: The goal of the present work is to detect for the first time pulsations in a rapidly rotating star seen nearly pole-on. <BR /> Methods: Vega was monitored in quasi-continuous high-resolution echelle spectroscopy. A total of 4478 spectra were obtained. More precisely in 2008 we obtained 1213 spectra during 19.9 h on 3 nights (26th, 27th and 29th of July 2008) with NARVAL/TBL (at R = 65 000 and R = 75 000), in 2009 we obtained 1293 spectra during 13.7 h on 3 nights (9th-11th of September 2009) with ESPaDOnS/CFHT (at R = 68 000) and in 2010 we gathered again 1972 with NARVAL/TBL during 28.8 h on five nights (July 15th-19th). This data set should represent the most extensive high S/N, high resolution quasi-continuous survey obtained on Vega as of today. Least square deconvolved (LSD) profiles were obtained for each spectrum representing the photospheric absorption profile potentially deformed by the presence of pulsations. In addition, we calculated for each spectrum a telluric line LSD profile subsequently used as radial velocity reference. LSD profile centroids were adjusted and velocity differences (stellar-telluric) determined. These residual velocities were analysed and periodic low amplitude variations, potentially indicative of stellar pulsations, detected. In a subsequent step, the temporal line profile variations during the longest (2010) data set was calculated for each individual velocity bin of 1.8 km s[SUP]-1[/SUP] by computing a 2D (velocity-frequency) Lomb-Scargle periodogram. <BR /> Results: Based on high resolution echelle spectroscopy, we have obtained indications of periodic variations of very small amplitudes within the residual radial velocity curves of Vega. All three data sets revealed the presence of residual periodic variations: 5.32 and 9.19 d[SUP]-1[/SUP] (A ≈ 6 m s[SUP]-1[/SUP]) in 2008, 12.71 and 13.25 d[SUP]-1[/SUP] (A ≈ 8 m s[SUP]-1[/SUP]) in 2009 and 5.42 and 10.82 d[SUP]-1[/SUP] (A ≈ 3-4 m s[SUP]-1[/SUP]) in 2010. However, it is too early to conclude that the variations are due to stellar pulsations, and a confirmation of the detection with a highly stable spectrograph is a necessary next step. <BR /> Conclusions: If pulsations are confirmed, their very small amplitudes show that the star would belong to a category of very "quiet" pulsators. Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France (CNRS), and at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, INSU/CNRS and the University of Hawaii. [less ▲]

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See detailDiscovery of a New AM CVn System with the Kepler Satellite
Fontaine, G.; Brassard, P.; Green, E. M. et al

in Astrophysical Journal (2011), 726

We report the discovery of a new AM CVn system on the basis of broadband photometry obtained with the Kepler satellite supplemented by ground-based optical spectroscopy. Initially retained on Kepler ... [more ▼]

We report the discovery of a new AM CVn system on the basis of broadband photometry obtained with the Kepler satellite supplemented by ground-based optical spectroscopy. Initially retained on Kepler target lists as a potential compact pulsator, the blue object SDSS J190817.07+394036.4 (KIC 004547333) has turned out to be a high-state AM CVn star showing the He-dominated spectrum of its accretion disk significantly reddened by interstellar absorption. We constructed new grids of NLTE synthetic spectra for accretion disks in order to analyze our spectroscopic observations. From this analysis, we infer preliminary estimates of the rate of mass transfer, the inclination angle of the disk, and the distance to the system. The AM CVn nature of the system is also evident in the Kepler light curve, from which we extracted 11 secure periodicities. The luminosity variations are dominated by a basic periodicity of 938.507 s, likely to correspond to a superhump modulation. The light curve folded on the period of 938.507 s exhibits a pulse shape that is very similar to the superhump wavefront seen in AM CVn itself, which is a high-state system and the prototype of the class. Our Fourier analysis also suggests the likely presence of a quasi-periodic oscillation similar to those already observed in some high-state AM CVn systems. Furthermore, some very low-frequency, low-amplitude aperiodic photometric activity is likely present, which is in line with what is expected in accreting binary systems. Inspired by previous work, we further looked for and found some intriguing numerical relationships between the 11 secure detected frequencies, in the sense that we can account for all of them in terms of only three basic clocks. This is further evidence in favor of the AM CVn nature of the system. [less ▲]

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See detailTowards ensemble asteroseismology of the young open clusters χ Persei and NGC 6910
Saesen, S.; Pigulski, A.; Carrier, F. et al

in Astronomische Nachrichten (2010), 331

As a result of the variability survey in χ Persei and NGC 6910, the number of β Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC 6910 and eleven in χ Persei ... [more ▼]

As a result of the variability survey in χ Persei and NGC 6910, the number of β Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC 6910 and eleven in χ Persei. We compare pulsational properties, in particular the frequency spectra, of β Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B-type stars in χ Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of β Cep-type stars and maybe also for other B-type pulsators. [less ▲]

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See detailThe PLATO End-to-End CCD Simulator -- Modelling space-based ultra-high precision CCD photometry for the assessment study of the PLATO Mission
Zima, W.; Arentoft, T.; De Ridder, J. et al

in Astronomische Nachrichten (2010, October 09), 331(9-10),

The PLATO satellite mission project is a next generation ESA Cosmic Vision satellite project dedicated to the detection of exo-planets and to asteroseismology of their host-stars using ultra-high ... [more ▼]

The PLATO satellite mission project is a next generation ESA Cosmic Vision satellite project dedicated to the detection of exo-planets and to asteroseismology of their host-stars using ultra-high precision photometry. The main goal of the PLATO mission is to provide a full statistical analysis of exo-planetary systems around stars that are bright and close enough for detailed follow-up studies. Many aspects concerning the design trade-off of a space-based instrument and its performance can best be tackled through realistic simulations of the expected observations. The complex interplay of various noise sources in the course of the observations made such simulations an indispensable part of the assessment study of the PLATO Payload Consortium. We created an end-to-end CCD simulation software-tool, dubbed PLATOSim, which simulates photometric time-series of CCD images by including realistic models of the CCD and its electronics, the telescope optics, the stellar field, the pointing uncertainty of the satellite (or Attitude Control System [ACS] jitter), and all important natural noise sources. The main questions that were addressed with this simulator were the noise properties of different photometric algorithms, the selection of the optical design, the allowable jitter amplitude, and the expected noise budget of light-curves as a function of the stellar magnitude for different parameter conditions. The results of our simulations showed that the proposed multi-telescope concept of PLATO can fulfil the defined scientific goal of measuring more than 20000 cool dwarfs brighter than mV =11 with a precision better than 27 ppm/h which is essential for the study of earth-like exo-planetary systems using the transit method. [less ▲]

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See detailPhotometric multi-site campaign on the open cluster NGC 884. I. Detection of the variable stars
Saesen, S.; Carrier, F.; Pigulski, A. et al

in Astronomy and Astrophysics (2010), 515

Context. Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further ... [more ▼]

Context. Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. <BR /> Aims: To improve our comprehension of the β Cep stars, we studied the young open cluster NGC 884 to discover new B-type pulsators, besides the two known β Cep stars, and other variable stars. <BR /> Methods: An extensive multi-site campaign was set up to gather accurate CCD photometry time series in four filters (U, B, V, I) of a field of NGC 884. Fifteen different instruments collected almost 77 500 CCD images in 1286 h. The images were calibrated and reduced to transform the CCD frames into interpretable differential light curves. Various variability indicators and frequency analyses were applied to detect variable stars in the field. Absolute photometry was taken to deduce some general cluster and stellar properties. <BR /> Results: We achieved an accuracy for the brightest stars of 5.7 mmag in V, 6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in the amplitude spectra is 50 μmag in the V band. Our campaign confirms the previously known pulsators, and we report more than one hundred new multi- and mono-periodic B-, A- and F-type stars. Their interpretation in terms of classical instability domains is not straightforward, pointing to imperfections in theoretical instability computations. In addition, we have discovered six new eclipsing binaries and four candidates as well as other irregular variable stars in the observed field. The photometric data of the variable stars are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A16">http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A16</A> [less ▲]

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See detailPost-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators
van Winckel, H.; Lloyd Evans, T.; Briquet, Maryline ULg et al

in Astronomy and Astrophysics (2009), 505

Context: The influence of binarity on the late stages of stellar evolution remains an open issue. <BR />Aims: While the first binary post-AGB stars were serendipitously discovered, the distinct ... [more ▼]

Context: The influence of binarity on the late stages of stellar evolution remains an open issue. <BR />Aims: While the first binary post-AGB stars were serendipitously discovered, the distinct characteristics of their spectral energy distribution (SED) allowed us to launch a more systematic search for binaries. We selected post-AGB objects, which exhibit a broad dust excess starting either at H or K, pointing to the presence of a gravitationally bound dusty disc in the system. We initiated an extensive multiwavelength study of those systems and here report on our radial velocity and photometric monitoring results for six stars of early F type, which are pulsators of small amplitude. <BR />Methods: To determine the radial velocity of low signal-to-noise ratio time-series data, we constructed dedicated autocorrelation masks based on high signal-to-noise ratio spectra, used in our published chemical studies. The radial velocity variations were analysed in detail to differentiate between pulsational variability and variability caused by orbital motion. When available, the photometric monitoring data were used to complement the time series of radial velocity data and to establish the nature of the pulsation. Finally, orbital minimalisation was performed to constrain the orbital elements. <BR />Results: All of the six objects are binaries with orbital periods ranging from 120 to 1800 days. Five systems have non-circular orbits. The mass functions range from 0.004 to 0.57 M[SUB]&sun;[/SUB] and the companions are probably unevolved objects of (very) low initial mass. We argue that these binaries must have evolved through a phase of strong binary interaction when the primary was a cool supergiant. Although the origin of the circumstellar disc is not well understood, the disc is generally believed to have formed during this strong interaction phase. The eccentric orbits of these highly evolved objects remain poorly understood. In one object, the line-of-sight grazes the edge of the puffed-up inner rim of the disc. <BR />Conclusions: These results corroborate our earlier statement that evolved objects in binary stars create a Keplerian dusty circumbinary disc. With the measured orbits and mass functions, we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems. based on observations collected with the Flemish 1.2 m Mercator telescope at Roque de los Muchachos (Spain), the Swiss 1.2 m Euler telescope at La Silla (Chile) and the 0.5 m and 0.75 m telescopes at SAAO (South-Africa). Tables [see full textsee full text]-[see full textsee full text] are only available in electronic form at http://www.aanda.org Postdoctoral fellow of the Fund for Scientific Research, Flanders. Ph.D. student of the Fund for Scientific Research, Flanders. [less ▲]

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See detailAn asteroseismic study of the β Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling
Desmet, M.; Briquet, Maryline ULg; Thoul, Anne ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different ... [more ▼]

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g-mode with frequency 0.3428d[SUP]-1[/SUP] reported before is detected in our spectroscopy. We identify the four main modes as (l[SUB]1[/SUB], m[SUB]1[/SUB]) = (1, 1), (l[SUB]2[/SUB], m[SUB]2[/SUB]) = (0, 0), (l[SUB]3[/SUB], m[SUB]3[/SUB]) = (1, 0) and (l[SUB]4[/SUB], m[SUB]4[/SUB]) = (2, 1) for f[SUB]1[/SUB] = 5.178964d[SUP]-1[/SUP], f[SUB]2[/SUB] = 5.334224d[SUP]-1[/SUP], f[SUB]3[/SUB] = 5.066316d[SUP]-1[/SUP] and f[SUB]4[/SUB] = 5.490133d[SUP]-1[/SUP], respectively. Our seismic modelling shows that f[SUB]2[/SUB] is likely the radial first overtone and that the core overshooting parameter α[SUB]ov[/SUB] is lower than 0.4 local pressure scale heights. [less ▲]

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See detailSpectroscopic observations of pulsating stars
Aerts, C.; Briquet, Maryline ULg; Carrier, F. et al

in Communications in Asteroseismology (2008), 157

During the past three decades, astronomers have been gathering extensive time series of high- precision spectroscopy of pulsating stars. In contrast to one-shot spectra, which provide the fundamental ... [more ▼]

During the past three decades, astronomers have been gathering extensive time series of high- precision spectroscopy of pulsating stars. In contrast to one-shot spectra, which provide the fundamental parameters, time-resolved spectroscopy offers a much broader variety of input for asteroseismology. The most important applications encompass the determination of the radial-velocity amplitudes and phases of the modes, the detection of modes that are invisible in photometry, the identification of the azimuthal orders through specialised methodology, the unravelling of pulsational and orbital motions, and, since a few years, the detection of solar-like oscillations in various types of stars. We discuss the input that spectroscopic time series can provide for asteroseismic modelling, for various types of pulsators. We end with some future prospects of how spectroscopy can help to push seismic applications beyond the present achievements. [less ▲]

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See detailClose-up of primary and secondary asteroseismic CoRoT targets and the ground-based follow-up observations
Uytterhoeven, K.; Poretti, E.; Rainer, M. et al

in Journal of Physics Conference Series (2008), 118

To optimise the science results of the asteroseismic part of the CoRoT satellite mission a complementary simultaneous ground-based observational campaign is organised for selected CoRoT targets. The ... [more ▼]

To optimise the science results of the asteroseismic part of the CoRoT satellite mission a complementary simultaneous ground-based observational campaign is organised for selected CoRoT targets. The observations include both high-resolution spectroscopic and multicolour photometric data. We present the preliminary results of the analysis of the ground-based observations of three targets. A line-profile analysis of 216 high-resolution FEROS spectra of the δ Sct star HD 50844 reveals more than ten pulsation frequencies in the frequency range 5-18 d[SUP]-1[/SUP], including possibly one radial fundamental mode (6.92 d[SUP]-1[/SUP]). Based on more than 600 multi-colour photometric datapoints of the β Cep star HD 180642, spanning about three years and obtained with different telescopes and different instruments, we confirm the presence of a dominant radial mode ν[SUB]1[/SUB] = 5.48695 d[SUP]-1[/SUP], and detect also its first two harmonics. We find evidence for a second mode ν[SUB]2[/SUB] = 0.3017 d[SUP]-1[/SUP], possibly a g-mode, and indications for two more frequencies in the 7-8 d[SUP]-1[/SUP] domain. From Stromgren photometry we find evidence for the hybrid 5 Sct/γ Dor character of the F0 star HD 44195, as frequencies near 3 d[SUP]-1[/SUP] and 21 d[SUP]-1[/SUP] are detected simultaneously in the different filters. [less ▲]

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See detailHigh-Precision Spectroscopy of Pulsating Stars
Aerts, C.; Hekker, S.; Desmet, M. et al

in Precision Spectroscopy in Astrophysics, Proceedings of the ESO/Lisbon/Aveiro Conference held in Aveiro, Portugal, 11-15 September 2006. (2008)

We review methodologies currently available to interprete time series of high-resolution high-S/N spectroscopic data of pulsating stars in terms of the kind of (non-radial) modes that are excited. We ... [more ▼]

We review methodologies currently available to interprete time series of high-resolution high-S/N spectroscopic data of pulsating stars in terms of the kind of (non-radial) modes that are excited. We illustrate the drastic improvement of the detection treshold of line-profile variability thanks to the advancement of the instrumentation over the past two decades. This has led to the opportunity to interprete line-profile variations with amplitudes of order m/s, which is a factor 1000 lower than the earliest line-profile time series studies allowed for. [less ▲]

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See detailLimits for the application of spectroscopic mode ID methods
Zima, W.; Kolenberg, K.; Briquet, Maryline ULg et al

in IAU Symposium, No. 224, The A-Star Puzzle, held in Poprad, Slovakia, July 8-13, 2004. (2004, December 01)

Spectroscopic mode identification techiques, which monitor intensity variations across an absorption line, provide the possibility of determining the quantum numbers l and m, the inclination and the ... [more ▼]

Spectroscopic mode identification techiques, which monitor intensity variations across an absorption line, provide the possibility of determining the quantum numbers l and m, the inclination and the intrinsic pulsation amplitude of a star. Of course, the uncertainties of the mode identification are dependent on the quality of the observations and the identification method applied. We have focused on the Pixel-by-pixel method/Direct line profile fitting (Mantegazza 2000) and the Moment method (Balona 1987, Briquet & Aerts 2003) for pinpointing mode parameters and tested the impact of various observational effects and stellar properties on the identification. [less ▲]

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See detailMoment Method and Pixel-by-Pixel Method: Complementary Mode Identification I. Testing FG Vir-like pulsation modes
Zima, W.; Kolenberg, K.; Briquet, Maryline ULg et al

in Communications in Asteroseismology (2004), 144

We have carried out a Hare-and-Hound test to determine the reliability of the Moment Method (Briquet & Aerts 2003) and the Pixel-by-Pixel Method (Mantegazza 2000) for the identification of pulsation modes ... [more ▼]

We have carried out a Hare-and-Hound test to determine the reliability of the Moment Method (Briquet & Aerts 2003) and the Pixel-by-Pixel Method (Mantegazza 2000) for the identification of pulsation modes in Delta Scuti stars. For this purpose we calculated synthetic line profiles, exhibiting six pulsation modes of low degree and with input parameters initially unknown to us. The aim was to test and increase the quality of the mode identification by applying both methods independently and by using a combined technique. Our results show that, whereas the azimuthal order m and its sign can be fixed by both methods, the degree l is not determined unambiguously. Both identification methods show a better reliability if multiple modes are fitted simultaneously. In particular, the inclination angle is better determined. We have to emphasize that the outcome of this test is only meaningful for stars having pulsational velocities below 0.2 vsini. This is the first part of a series of articles, in which we will test these spectroscopic identification methods. [less ▲]

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