arXiv subjects

H. Meusinger

Publications and source records attributed to H. Meusinger.

34 records · Page 2Linked to original sources

arXiv2007

A systematic search for novae in M31 on a large set of digitized archival Schmidt plates

This paper reports on the detection of optical novae in our neighbour galaxy M31 based on digitized historical Tautenburg Schmidt plates. The accurate positions of the detected novae lead to a much larger database when searching for recurrent novae in M31. We conducted a systematic search for novae on 306 digitized Tautenburg Schmidt plates covering a time span of 36 years from 1960 to 1996. From the database of both ~ 300 000 light curves and about one million detections on only one plate per colour band, nova candidates were efficiently selected by automated algorithms and subsequently individually inspected by eye. We report the detection of 84 nova candidates. We found 55 nova candidates from the automated analysis of the light curves. Among these, 22 were previously unknown, 12 were known but not identified on Tautenburg Schmidt plates before, and 21 novae had been previously discovered on Tautenburg plates. An additional 29 known novae could be confirmed by the detailed investigation of single detections. One of our newly discovered nova candidates shows a high position coincidence with a nova detected about 30 years earlier. Therefore, this object is likely to be a recurrent nova. Furthermore, we re-investigated all 41 nova candidates previously found on Tautenburg plates and confirm all but two. Positions are given for all nova candidates with a typical accuracy of ~ 0.4 arcsec. We present light curves and finding charts as online material. The analysis of the plates has shown the wealth of information still buried in old plate archives. Extrapolating from this survey, digitization of other historical M31 plate archives (e.g. from the Mount Wilson or Asiago observatories) for a systematic nova search looks very promising.

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arXiv2007

FSR0190 - Another old distant galactic cluster

We are conducting a large program to classify newly discovered Milky Way star cluster candidates from Froebrich et al. (2007). Here we present NIR follow-up observations of FSR0190 (RA=20h05m31.3s, DEC=33deg34'09" J2000). The cluster is situated close to the Galactic Plane (l=70.7302deg, b=+0.9498deg). It shows a circular shape, a relatively large number of core helium burning stars -- which clearly distinguishes the cluster from the rich field -- but no centrally condensed star density profile. We derive an age of more than 7Gyr, a Galactocentric distance of 10.5kpc, a distance of 10kpc from the Sun, and an extinction of A_K=0.8mag. The estimated mass is at least of the order of 1E5M_sun, and the absolute brightness is M_V<=-4.7mag; both are rather typical properties for Palomar-type globular clusters.

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arXiv2007

The reddest ISO-2MASS quasar

In the course of the NIR/MIR AGN search combining the 6.7 mu ISOCAM Parallel Survey and 2MASS we have discovered 24 type-1 quasars about a third of which are too red to be discriminated by optical/UV search techniques. Here we report on a detailed case study of the reddest type-1 quasar of our sample (J2341) at redshift z=0.236 with M_K=-25.8 and J-K=1.95. We performed spectroscopy in the optical with VLT/FORS1 and in the MIR with Spitzer as well as NIR imaging with ISPI at CTIO. The optical and NIR observations reveal a star forming emission-line galaxy at the same redshift as the quasar with a projected linear separation of 1.8 arcsec (6.7 kpc). The quasar and its companion are embedded in diffuse extended continuum emission. Compared with its companion the quasar exhibits redder optical-NIR colours, which we attribute to hot nuclear dust. The MIR spectrum shows only few emission lines superimposed on a power-law spectral energy distribution. However, the lack of strong FIR emission suggests that our potentially interacting object contains much less gas and dust and is in a stage different from dust reddened ULIRG-AGN like Mrk 231. The optical spectrum shows signatures for reddening in the emission-lines and no post-starburst stellar population is detected in the host galaxy of the quasar. The optical continuum emission of the active nucleus appears absorbed and diluted. Even the combination of absorption and host dilution is not able to match J2341 with standard quasar templates. While the BLR shows only a rather moderate absorption of E_(B-V)=0.3, the continuum shorter than 4500 AA requires strong obscuration with E_(B-V)=0.7, exceeding the constraints from the low upper limit on the 9.7 mu silicate absorption. This leads us to conclude that the continuum of J2341 is intrinsically redder than that of typical quasars.

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arXiv2007

FSR1735 -- A new globular cluster candidate in the inner Galaxy

We carry out a large program to classify newly discovered star clusters from Froebrich et al. (2006) in the inner Galaxy. Here, we present a first analysis of a new high-priority globular cluster candidate, FSR1735 at l=339.1879; b=-1.8534, based on new deep near infrared observations from Sofi at the NTT. A significant peak in the K-band luminosity function is found, which is interpreted as the clump of post-He-flash stars. The distance and the reddening of the cluster are determined to 9.1kpc and A_K=0.5mag, respectively, the metallicity is estimated to [M/H]=-0.8. Radial star density profiles are used to measure the core radius and the tidal radius of the cluster. The lack of signs for on-going star formation and the position in the Galaxy pose strong arguments against the interpretation of this object as a young or old open cluster. All the observational evidence is in agreement with the interpretation that FSR1735 is a so far unknown globular cluster in the inner Galaxy.

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arXiv2007

The inner structure of the S0 galaxy NGC3384

We re-investigate the lenticular galaxy NGC 3384, a member of the LeoI galaxy group, using HST and multi-colour Calar Alto observations. Various approaches are used to visualize the two known peculiar components, the so-called inner component (IC) and the elongated component (EC), on the HST images. The methods were checked in detail using synthetical images from simulated galaxies. For the first time, we make the IC as well as the inner part of the EC visible on direct images. The results confirm both the bar-like appearance of the inner EC and the quasi-elliptical shape of the IC. The IC resembles an inclined disk where the surface brightness becomes successively shallower towards the centre compared to an exponential profile. The orientation of the inner part of the EC is perpendicular to the major axis of the IC. The broad-band colour indices are shown to be in agreement with model predictions for a 5 to 7 Gyr old stellar population of quasi-solar metallicity. No significant large-scale variations of the colour indices over the main body of the galaxy are found. We discuss the previously reported colour gradients close to the nucleus and argue that the most plausible explanation is reddening by small amounts of dust though unsharpe masked HST images do not provide significant hints for clumpy dust. According to the episodic dust settling scenario suggested by Lauer et al (2005), the very low dust fraction indicates that NGC3384 is in a post-activity phase and at the beginning of a new dust-settling cycle.

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arXiv2007

Narrow-line AGN in the ISO-2MASS Survey

Context: A long-standing challenge of observational AGN research is to find type 2 quasars, the luminous analogues of Seyfert-2 galaxies. Aims: We search for luminous narrow-line type 2 AGN, characterise their properties, and compare them with broad-line type 1 AGN. Methods: Combining the ISOCAM parallel survey at 6.7 mu with 2MASS, we have selected AGN via near-mid-infrared colours caused by the hot nuclear dust emission. We performed spectroscopy in the optical and, for a subset of the sample, also in the mid-infrared with Spitzer. Results: We find nine type 2 AGN at redshift 0.1 0.5 we did not find type 2 AGN, probably because the hottest dust emission, still covered by the NIR filters, is obscured. The optical spectra of the type 2 host galaxies show young and old stellar populations. Only one object is an ultraluminous infrared galaxy with starburst. The 5-38 mu spectra of the two type 2 sources observed show a strong continuum with PAH emission in one case and silicate absorption in the other case. Conclusions: The near-mid-infrared selection is a successful strategy to find luminous type 2 AGN at low z. The objects exhibit a large range of properties so that it is difficult to infer details by means of popular SED fitting with simple average templates.

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arXiv2006

The new nebula in LDN 1415 - A cry from the cradle of a low-luminosity source

A survey for candidate Herbig-Haro objects was performed to search for evidence of star formation in Galactic dark clouds. For this aim true colour images were created from blue, red, and infrared DSS2 plates and inspected. Follow-up I-band, Halpha, and [SII] CCD imaging and long-slit spectroscopy using the Tautenburg 2-m telescope was carried out to verify candidate objects. In the case of LDN 1415, the presence of a Herbig-Haro flow could be revealed which is henceforth named HH 892. In addition, an arcuate nebula was found which is barely seen on the DSS2 infrared plate (epoch 1996) and not detected in archival Kiso Schmidt data (epoch 2001). Thus, this nebula must have brightened by about 3.8mag in recent years.The nebula is associated with IRAS 04376+5413. The 2MASS images show a red counterpart of the IRAS source, designated as L1415-IRS. Its morphology resembles that of a bipolar young object. The luminosity of this source integrated from 0.9micron to 60micron in the low state amounts to 0.13L_sun for an assumed distance of 170pc. Thus it seems to be a young very-low mass star or it might even be of substellar mass. The current brightness increase of the nebula is caused by a FUor- or EXor-like outburst as indicated by the presence of a P Cygni profile of the Halpha line. L1415-IRS is by far the least luminous member of the sparse sample of FUor and EXor objects.

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arXiv2005

The ISO-2MASS AGN survey: On the type-1 sources

We combined the ISOCAM Parallel Mode Survey at 6.7 micron (LW2 filter) with the Two Micron All Sky Survey in order to obtain a powerful tool to search for AGN independent of dust extinction. Using moderate colour criteria H-K>0.5 and K-LW2>2.7 we have selected a sample of 77 AGN candidates in an effective area of about 10 square degrees. By means of optical spectroscopy we find 24 (30%) type-1 QSOs at redshifts 0.1 0.8. About one third of the ISO-2MASS QSOs show so red optical colours, that they are missed in optical and UV AGN surveys like SDSS, 2DF, or HES. With a surface density of about 2 deg^(-2) down to R<18 mag the ISO-2MASS QSOs outnumber the 1.35 deg^(-2) of the SDSS quasar survey by 50%; we find a combined optical-IR QSO surface density of 2.7 deg^(-2). Since only two of the ISO-2MASS QSOs have also J-K>2, the inclusion of the ISO mid-infrared photometry significantly extends the capabilities of the pure 2MASS red AGN survey. We suggest that the newly found red AGN resemble young members of the quasar population, and that quasars spend much of their lifetime in a dust enshrouded phase.

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arXiv2005

VPMS J1342+2840 - an unusual quasar from the variability and proper motion survey

We report the discovery of the highly peculiar, radio-loud quasar VPMS J1342+2840 (z ~ 1.3) from the variability and proper motion survey. We present spectroscopic, imaging and photometric observations. The unusual spectrum shows a strong depression of the continuum over a wide wavelength range in the blue part without the typical structures of broad absorption line (BAL) troughs. The image of the quasar is unresolved and there is no evidence for a foreground object on the line of sight. The broad-band spectral energy distribution is not consistent with obvious dust reddening with the standard SMC extinction curve. The downturn of the continuum flux of VPMS J1342+2840 at short wavelengths can be caused by dust reddening only if the reddening curve is steeper then the SMC curve in the ultraviolet and is very flat at longer wavelengths. Alternatively, the dominant spectral features can be explained by low-ionization BALs forming unusually wide, overlapping absorption troughs.

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arXiv2004

High-Resolution NIR Observations of the Circumstellar Disk System in the Bok Globule CB 26

We report on results of near-infrared and optical observations of the mm disk embedded in the Bok globule CB 26 (Launhardt & Sargent 2001). The near-infrared images show a bipolar reflection nebula with a central extinction lane which coincides with the mm disk. Imaging polarimetry of this object yielded a polarization pattern which is typical for a young stellar object surrounded by a large circumstellar disk and an envelope, seen almost edge-on. The strong linear polarization in the bipolar lobes is caused by single scattering at dust grains and allowed to locate the illuminating source which coincides with the center of the mm disk. The spectral energy distribution of the YSO embedded in CB 26 resembles that of a ClassI source with a luminosity of 0.5 L_sun.Using the pre-main-sequence evolutionary tracks and the stellar mass inferred from the rotation curve of the disk, we derive an age of the system of <10^6 yr. H_alpha and [SII] narrow-band imaging as well as optical spectroscopy revealed an Herbig-Haro object 6.15 arcmin northwest of CB 26 YSO 1, perfectly aligned with the symmetry axis of the bipolar nebula. This Herbig-Haro object (HH 494) indicates ongoing accretion and outflow activity in CB 26 YSO 1. Its excitation characteristics indicate that the Herbig-Haro flow is propagating into a low-density environment. We suggest that CB 26 YSO 1 represents the transition stage between embedded protostellar accretion disks and more evolved protoplanetary disks around T Tauri stars in an undisturbed environment.

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arXiv2003

A Complete Sample of Soft X-ray Selected AGN: I. The Data

We present the optical spectra and simple statistical analysis for a complete sample of 110 soft X-ray selected AGN. About half of the sources are Narrow-Line Seyfert 1 galaxies (NLS1s), which have the steepest X-ray spectra, strongest FeII emission and slightly weaker [OIII]5007 emission than broad line Seyfert 1s (BLS1s). Kolmogorov Smirnov tests show that NLS1s and BLS1s have clearly different distributions of the X-ray spectral slope, X-ray short-term variability, and FeII equivalent widths and luminosity and FeII/H-beta ratios. The differences in the [OIII]/H-beta and [OIII] equivalent widths are only marginal. We found no significant differences between NLS1s and BLS1s in their rest frame 0.2-2.0 X-ray luminosities, rest frame 5100A monochromatic luminosities, bolometric luminosities, redshifts, and their H$β$ equivalent widths.

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arXiv2002

QSOs from the variability and proper motion survey in the M3 field

We present results of the spectroscopical follow-up observations of QSO candidates from a combined variability and proper motion (VPM) survey in a ~10 square degrees region centered on the globular cluster M3. The search is based on a large number of digitised Schmidt plates with a time-baseline of three decades. This paper reviews the candidate selection, the follow-up spectroscopy, and general properties of the resulting QSO sample. In total, 175 QSOs and Sey1s were identified among the objects from the VPM survey, with 114 QSOs and 10 Sey1s up to the pre-estimated 90% completeness limit of the survey at B_lim~19.7. The redshift range of the QSOs is 0.4<z<3. Among the 80 QSO candidates of highest priority we confirm 75 QSOs/Sey1s and 2 NELGs. We present magnitudes, colours, redshifts, and variability indices for all 181 identified QSOs/Sey1s/NELGs and spectra for the 77 QSOs/Sey1s/NELGs from our spectroscopic follow-up observations. The VPM survey uses selection criteria that are not directly relying on the spectral energy distribution of QSOs. It is therefore remarkable that the properties of the VPM QSOs do not significantly differ from those of samples from colour selection or slitless spectroscopy. In particular, we do not detect a substantial number of unusually red QSOs. The total surface density of the brighter QSOs (17<=B<=18.5) in our search field is found to be by a factor of ~1.8 larger than that derived from previous optical surveys.

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arXiv2002

A QSO survey via optical variability and zero proper motion in the M92 field. IV. More QSOs due to improved photometry

We continue the QSO search in the 10 square degrees Schmidt field around M92 based on variability and proper motion (VPM) constraints. We have re-reduced 162 digitised B plates with a time-baseline of more than three decades and have considerably improved both the photometric accuracy and the star-galaxy separation at B>19. QSO candidates are selected and marked with one out of three degrees of priority based on the statistical significance of their measured variability and zero proper motion. Spectroscopic follow-up observations of 84 new candidates with B>19 revealed an additional 37 QSOs and 7 Seyfert1s. In particular, all 92 high-priority candidates are spectroscopically classified now; among them are 70 QSOs and 9 Seyfert1s (success rate 86%). We expect that 87% (55%) of all QSOs with B<19.0 (19.8) are contained in this high-priority subsample. For the combined sample of high-priority and medium-priority objects, a completeness of 89% is estimated up to B_lim=19.5. The sample of all AGNs detected in the framework of the VPM search in the M92 field contains now 95 QSOs and 14 Seyfert1s with B<19.9. Although the VPM QSOs were selected by completely different criteria, their properties do not significantly differ from those of QSOs found by more traditional optical survey techniques. In particular, the spectra and the optical broad band colours do not provide any hints on a substantial population of red QSOs up to the present survey limit.

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arXiv2002

A QSO survey via optical variability and zero proper motion in the M92 field.III. Narrow emission line galaxies

We study a sample of 23 narrow-emission line galaxies (NELGs) which were selected by their strong variability as QSO candidates in the framework of a variability-and-proper motion QSO survey on digitised Schmidt plates. In previous work, we have shown that variability is an efficient method to find AGNs. The variability properties of the NELGs are however significantly different from those of the QSOs. The main aim of this paper is to clarify the nature of this variability and to estimate the fraction of AGN-dominated NELGs in this sample. New photometric and spectroscopic observations are presented, along with revised data from the photographic photometry. The originally measured high variability indices could not be confirmed. The diagnostic line-ratios of the NELG spectra are consistent with HII region-like spectra. No AGN could be proved, yet we cannot rule out the existence of faint low-luminosity AGNs masked by HII regions from intense star formation.

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arXiv2001

The merger stage of the ultra-luminous infrared galaxy IRAS 03158+4227

We examine the merger stage of IRAS 03158+4227, one of the most luminous ULIRGs from the IRAS 2 Jy sample. Deep optical images are presented along with high-resolution NIR images and optical low-resolution spectra. IRAS 03158+4227 is confirmed as a component of an equal-luminosity binary galaxy with a nuclei separation of 47 / (h/75) kpc. A long lopsided tail emanating from the companion, which harbours an active nucleus, is the most prominent peculiar feature of the binary. The results of numerical simulations admit the interpretation of this structure as a product of the tidal interaction between the two components. If the infrared-activity of IRAS 03158+4227 is also dynamically triggered by this process, this would implicate that the ULIRG phenomenon is not restricted to the final stage of a binary merger. Alternatively, the system may be a multiple merger where the partner(s) has/have already coalesced.

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arXiv2001

Search for nearby stars among proper motion stars selected by optical-to-infrared photometry. I. Discovery of LHS 2090 at spectroscopic distance of d=6pc

We present the discovery of a previously unknown very nearby star - LHS 2090 at a distance of only d=6 pc. In order to find nearby (i.e. d < 25 pc) red dwarfs, we re-identified high proper motion stars ($μ>$ 0.18 arcsec/yr) from the NLTT catalogue (Luyten \cite{luyten7980}) in optical Digitized Sky Survey data for two different epochs and in the 2MASS data base. Only proper motion stars with large $R-K_s$ colour index and with relatively bright infrared magnitudes ($K_s<10$) were selected for follow-up spectroscopy. The low-resolution spectrum of LHS 2090 and its large proper motion (0.79 arcsec/yr) classify this star as an M6.5 dwarf. The resulting spectroscopic distance estimate from comparing the infrared $JHK_s$ magnitudes of LHS 2090 with absolute magnitudes of M6.5 dwarfs is $6.0\pm1.1$ pc assuming an uncertainty in absolute magnitude of $\pm$0.4 mag.

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