[Paper Review] The Missing CV Population: Results From An Objective Prism Survey

C. Tappert, T. Augusteijn+1 more|arXiv (Cornell University)|Sep 28, 2001

Astrophysics and Cosmic Phenomena3 citations

TL;DR

This study conducts an objective prism survey of the southern sky to detect faint, evolved cataclysmic variables (CVs) predicted by theory but missing in observations. Despite identifying 21 CVs—12 previously unknown—the lack of a significant pile-up at the observed minimum period (~78 min) suggests the theoretical prediction of a large population of low-mass-transfer CVs may be incorrect, challenging current evolutionary models.

ABSTRACT

We present the results of a search for cataclysmic variables (CVs) in the Calan-Tololo survey. We detected a total number of 21 CVs, 12 of them are previously unknown objects. Our results suggest that the mismatch between the theoretically predicted sample and the observed one is not due to observational bias but has to be resolved by a revision of the theoretical models.

Motivation & Objective

• To test whether the theoretical prediction of a large population of low-mass-transfer CVs is observationally supported.
• To investigate the discrepancy between the theoretically predicted minimum orbital period (P_min,the ~65 min) and the observed minimum period (P_min,obs ~78 min).
• To determine if the 'missing' CV population—expected to be faint and long-period—can be detected via spectroscopic surveys.
• To assess whether observational bias or flaws in theoretical models explain the mismatch between predicted and observed CV populations.
• To evaluate the completeness and reliability of visual inspection in objective prism surveys for detecting evolved CVs.

Proposed method

• Utilized the Calán-Tololo objective prism survey (CTS), covering 5150 deg² of the southern sky with |b| ≥ 20°, reaching a limiting magnitude of ~18.5.
• Conducted visual inspection of ~half of the CTS plates to identify 59 candidate CVs based on spectral appearance.
• Performed follow-up medium-resolution spectroscopy, calibrated photometry, and time-series photometry for all newly identified objects.
• Applied time-resolved spectroscopy to selected CVs to confirm their nature and measure orbital periods.
• Compared the period distribution of detected CVs with the Ritter & Kolb (1998) catalogue, restricting analysis to non-magnetic CVs at |b| > 20° to minimize bias.
• Quantified sample completeness and contamination risks due to subjective visual selection, acknowledging inherent observer bias.

Experimental results

Research questions

• RQ1 Are the missing low-mass-transfer CVs—predicted by theory but not observed—detectable using objective prism surveys?
• RQ2 Does the observed period distribution of CVs in high galactic latitude regions show a pile-up at P_min,obs ~78 min, as expected from theoretical models?
• RQ3 To what extent does the visual inspection method in objective prism surveys introduce bias against detecting evolved, faint CVs?
• RQ4 Is the discrepancy between theoretical predictions and observational data due to observational limitations or flaws in theoretical models of CV evolution?
• RQ5 How many previously unknown CVs can be discovered in a deep, wide-area spectroscopic survey, and what are their orbital period characteristics?

Key findings

• The survey identified 21 CVs, including 12 previously unknown objects, from a sample of 59 visually selected candidates.
• The period distribution of the detected CVs shows no significant pile-up at the observed minimum period (P_min,obs ~78 min), and the peak is even less pronounced than in the known sample.
• The number of newly discovered CVs is insufficient to resolve the theoretical-observational mismatch, indicating the missing population is likely smaller than predicted.
• Despite potential biases in visual inspection, the failure to detect a large number of evolved CVs suggests their actual population may be much smaller than theoretical models predict.
• The lack of detection of faint, long-period CVs—despite their expected strong emission lines—supports the conclusion that theoretical models may require revision.
• The results align with Patterson (1998) in suggesting that the mismatch between theory and observation is not due to observational bias but may stem from incorrect assumptions in theoretical models of CV evolution.