The stellar population of the Rosat North Ecliptic Pole survey

Micela, G.; Affer, L.; Favata, F.; Henry, J. P.; Gioia, I. M.; Mullis, C. R.; Sanz-Forcada, J.; Sciortino, S.

doi:10.1051/0004-6361:20066146

Cited by 12 publications

(15 citation statements)

References 32 publications

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“…We inspected the optical spectra of all Galactic NEP sources, and found only two additional objects with the spectral appearance of interacting binaries. A more detailed study of stellar sources included in the survey has yielded accurate spectral classifications of all stellar NEP sources (Micela et al 2007), and no additional CV candidates. We are therefore confident that we have identified every CV in the NEP sample.…”

Section: Cvs In the Rosat Nep Surveymentioning

confidence: 99%

The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey

Pretorius¹,

Knigge²,

O’Donoghue³

et al. 2007

Monthly Notices of the Royal Astronomical Society

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We use the ROSAT North Ecliptic Pole (NEP) survey to construct a small, but purely X‐ray flux‐limited sample of cataclysmic variable stars (CVs). The sample includes only four systems, two of which (RX J1715.6+6856 and RX J1831.7+6511) are new discoveries. We present time‐resolved spectroscopy of the new CVs and measure orbital periods of 1.64 ± 0.02 and 4.01 ± 0.03 h for RX J1715.6+6856 and RX J1831.7+6511, respectively. We also estimate distances for all the CVs in our sample, based mainly on their apparent brightness in the infrared. The space density of the CV population represented by our small sample is 1.1+2.3−0.7× 10−5 pc−3. We can also place upper limits on the space density of any subpopulation of CVs too faint to be included in the NEP survey. In particular, we show that if the overall space density of CVs is as high as 2 × 10−4 pc−3 (as has been predicted theoretically), the vast majority of CVs must be fainter than LX≃ 2 × 1029 erg s−1.

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Section: Cvs In the Rosat Nep Surveymentioning

confidence: 99%

The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey

Pretorius¹,

Knigge²,

O’Donoghue³

et al. 2007

Monthly Notices of the Royal Astronomical Society

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“…A possible explanation in terms of binary systems with a yellow primary star and a secondary M dwarf, which responsible for the X-ray emission, was proposed by Micela et al (2007). However, this does not explain the apparent excess of stars with high X-ray fluxes detected in the log N− log S diagram ).…”

Section: Introductionmentioning

confidence: 97%

Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association

López‐Santiago

Micela

Montes

2009

A&A

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Context. The associations and moving groups of young stars are excellent laboratories for investigating stellar formation in the solar neighborhood. Previous results have confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of young stellar kinematic groups. A detailed study of the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, and identify the origin of these structures. Aims. Our intention is to characterize members of the young moving groups, determine their age distribution, and quantify the contamination by old main-sequence stars, in particular, for the Local Association. Methods. We used stars possible members of the young (∼10-650 Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line Li i λ6707.8 Å and H α , to constrain the range of ages of the stars.Results. By combining photometric and spectroscopic data, we were able to separate the young stars (10−650 Myr) from the old (>1 Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ∼30%. This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with <200 Myr and stars older than this. Conclusions. Among the candidate members of the classical moving groups, there is a non-negligible fraction of old field stars that should be taken into account when studying the stellar birthrate in the solar neighborhood. Our results are consistent with a scenario in which the moving groups contain both groups of young stars formed in a recent star-formation episode and old field stars with similar space motion. Only by combining X-ray and optical spectroscopic data is it possible to distinguish between these two age populations.

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“…In this new era of Virtual Observatory and extensive photometric databases and catalogs, the compilation of spectroscopic data is important for the purpose of constraining the properties of different astronomical objects, in particular, of stars (e.g. Sciortino et al 1995;Takeda et al 2007;Micela et al 2007;López-Santiago et al 2007;Klutsch et al 2008;López-Santiago et al 2009). The utility of substantial spectroscopic compilations has been demonstrated in the past by various groups.…”

Section: Introductionmentioning

confidence: 99%

A high-resolution spectroscopic survey of late-type stars: chromospheric activity, rotation, kinematics, and age

López‐Santiago¹,

Montes²,

Galvez-Ortiz

et al. 2010

A&A

100

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Aims. We present a compilation of spectroscopic data from a survey of 144 chromospherically active young stars in the solar neighborhood, which may be used to investigate different aspects of its formation and evolution in terms of kinematics and stellar formation history. The data have already been used by us in several studies. With this paper, we make all these data accessible to the scientific community for future studies on different topics. Methods. We performed spectroscopic observations with echelle spectrographs to cover the entirety of the optical spectral range simultaneously. Standard data reduction was performed with the IRAF echelle package. We applied the spectral subtraction technique to reveal chromospheric emission in the stars of the sample. The equivalent width of chromospheric emission lines was measured in the subtracted spectra and then converted to fluxes using equivalent width-flux relationships. Radial and rotational velocities were determined by the cross-correlation technique. Kinematics, equivalent widths of the lithium line λ6707.8 Å and spectral types were also determined. Results. A catalog of spectroscopic data is compiled: radial and rotational velocities, space motion, equivalent widths of optical chromospheric activity indicators from Ca ii H & K to the calcium infrared triplet and the lithium line in λ6708 Å. Fluxes in the chromospheric emission lines and R HK are also determined for each observation of a star in the sample. We used these data to investigate the emission levels of our stars. The study of the Hα emission line revealed two different populations of chromospheric emitters in the sample, clearly separated in the log F Hα /F bol − (V − J) diagram. The dichotomy may be associated with the age of the stars.

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The stellar population of the Rosat North Ecliptic Pole survey

Cited by 12 publications

References 32 publications

The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey

The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey

Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association

A high-resolution spectroscopic survey of late-type stars: chromospheric activity, rotation, kinematics, and age

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