-
[show abstract]
[hide abstract]
ABSTRACT: Aims. The aim of this work is to further investigate the nature of PAH
excitation and emission especially in the context of tracing star formation in
a variety of extragalactic environments. Here we turn our attention to the
energetic environment of the closest AGN in our sample, Centaurus A. Methods.
Using ISAAC on the ESO VLT UT1 (Antu) we have made high spatial resolution 3.3
{\mu}m imaging observations of the central kiloparsec of CenA. These
observations have been compared with star formation tracers in the near- and
mid-infrared, as well as with mid-infrared tracers of nuclear activity.
Results. The nucleus is not devoid of PAH emission, implying that the PAH
particles are not destroyed in the nucleus as might be expected for such a
harsh environment. However, we see the feature to continuum ratio decrease
towards the AGN. As well, the 3.3 {\mu}m PAH feature emission generally traces
the sites of star formation in Cen A, but in detail there are spatial offsets,
consistent with an earlier study of the starburst galaxies NGC 253 and NGC
1808. However, the feature-to-continuum ratio does not drop at the positions of
star formation as was previously seen in that earlier study. The cause for this
difference remains uncertain. Finally, our data reveal possible evidence for a
nearly face-on, circular or spiral, dust structure surrounding the nucleus.
02/2013;
-
[show abstract]
[hide abstract]
ABSTRACT: We report near-infrared integral field spectroscopy of the luminous merging galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by 16 are the central parts of inclined, rotating disk galaxies with equal mass bulges. The dynamical masses of the nuclei are much larger than the stellar mass derived from the K-band light, implying that the progenitor galaxies were galaxies with massive bulges. The K-band light is dominated by red supergiants formed in the two nuclei in starbursts, triggered ≈2 × 107 yr ago, possibly by the most recent perigalactic approach. Strong feedback effects of a superwind and supernovae are responsible for a short duration burst (≈5 × 106 yr) that is already decaying. The two galaxies form a prograde-retrograde rotating system and from the stellar velocity field it seems that one of the two interacting galaxies is subject to a prograde encounter. Between the stellar nuclei is a prominent peak of molecular gas (H2, CO). The stellar velocity dispersion peaks there indicating that the gas has formed a local, self-gravitating concentration decoupled from the stellar gravitational potential. NGC 6240 has previously been reported to fit the paradigm of an elliptical galaxy formed through the merger of two galaxies. This was based on the near-infrared light distribution, which follows a r1/4-law. Our data cast strong doubt on this conclusion: the system is by far not relaxed, rotation plays an important role, as does self-gravitating gas, and the near-infrared light is dominated by young stars.
The Astrophysical Journal 12/2008; 537(1):178. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present deep 1.6 (H) and 2.2μm (K) images of the central parsec of the Galaxy at a resolution of 0.15″. We also give a
brief history of high spatial resolution imaging of the Galactic Center in the near-infrared. Our recent speckle imaging results
are: Most of the flux in earlier seeing limited images comes from about 340 unresolved stellar sources with K magnitudes <14.
Most of the fainter stars in the central parsec are likely to be M-rather than K-giants. The IRS 16 and 13 complexes are resolved
into about 25 and 6 sources, many of which are probably luminous hot stars. We confirm the presence of a blue near infrared
object (K≈13) at the position of the compact radio source Sgr A*. This source either has a ∼0.5" east-west size or it is multiple with its western component closest to Sgr A*. The spatial centroid of the number distribution of compact sources is consistent with the position of Sgr A* but not with a position in the IRS 16 complex. The stellar surface density is very well fitted by an isothermal cluster model
with a core radius of 0.15±0.05 pc. If the 2μm emitting stars sample the overall mass distribution of the stellar cluster
the stellar density is a few times 107 M⊙ pc−3. Buildup of massive stars by collisional merging of lower mass stars and collisional disruption of giant atmospheres are
very probable processes in the central 0.2pc.
01/2007: pages 41-49;
-
[show abstract]
[hide abstract]
ABSTRACT: The first ESO adaptive optics system instrument, NACO, installed at the VLT has been offered to the astronomical community
and used on a regular basis in service and visitor mode for just over one year. We present an overview of the first year of
operations and an analysis of some NACO technical and calibration data.
09/2005: pages 53-61;
-
[show abstract]
[hide abstract]
ABSTRACT: We report R~3000 VLT ISAAC K-band spectroscopy of the nuclei (i.e. central 100-300pc) of 9 galaxies hosting an active galactic nucleus. For 5 of these we also present spectra of the circumnuclear region out to 1kpc. We have measured a number of H_2 lines in the v=1-0, 2-1, and 3-2 vibrational transitions, as well as the Br_gamma and HeI recombination lines, and the NaI stellar absorption. Although only 3 of the galaxies are classified as Seyfert 1s in the literature, broad Br_gamma (FWHM 1000kms) is seen in 7 of the objects. The v=1-0 emission appears thermalised at T~1000K. However, the v=2-1 and 3-2 emission show evidence of being radiatively excited by far-UV photons. The PDR models that fit the data best are, as for the ultraluminous infrared galaxies in Davies et al. (2003), those for which the H_2 emission arises in dense clouds illuminated by intense FUV radiation. The NaI stellar absorption is clearly seen in 6 of the nuclear spectra, indicating the presence of a significant population of late type stars. It is possible that these stars are a result of the same episode of star formation that gave rise to the stars heating the PDRs. It seems unlikely that the AGN is the dominant source of excitation for the near infrared H_2 emission: in two nuclei H_2 was not detected at all, and in general we find no evidence of suppression of the 2-1S(3) line, which may occur in X-ray irradiated gas. Our data do not reveal any significant difference between the nuclear and circumnuclear line ratios, suggesting that the physical conditions of the dominant excitation mechanism are similar both near the AGN and in the larger scale environment around it, and that star formation is an important process even in the central 100pc acround AGN. Comment: accepted for publication in ApJ (32 pages, 12 figures)
07/2005;
-
[show abstract]
[hide abstract]
ABSTRACT: We report on new high-resolution near-infrared images of the gravitationally lensed radio source PKS1830-211, a quasar at z=2.507. These adaptive optics observations, taken with the Very Large Telescope (VLT), are further improved through image deconvolution. They confirm the presence of a second object along the line of sight to the quasar, in addition to the previously known spiral galaxy. This additional object is clearly extended in our images. However, its faint luminosity does not allow to infer any photometric redshift. If this galaxy is located in the foreground of PKS1830-211, it complicates the modeling of this system and decreases the interest in using PKS1830-211 as a means to determine H0 via the time delay between the two lensed images of the quasar. Comment: Accepted in A&A Letters
06/2005;
-
[show abstract]
[hide abstract]
ABSTRACT: (ABRIDGED) We have undertaken a programme of 3 micron narrowband imaging of a sample of nearby template galaxies covering a wide range of metallicity, star formation activity, and nuclear activity. In the present paper we present first results: high spatial resolution images of PAH emission and the adjacent continuum emission from the central regions of the nearby starburst galaxies NGC253 and NGC1808. Globally, the PAH emission is seen to peak on the central starburst regions of both sources. On smaller scales, however, we see no general spatial correlation or anti-correlation between the PAH emission and the location of sites of recent star formation, suggesting that the degree to which PAH emission traces starburst activity is more complicated than previously hypothesized based on results from data with lower spatial resolution. We do find spatial correlations, though, when we consider the PAH-to-continuum ratio, which is low at the positions of known super star clusters in NGC1808 as well as at the position of the IR peak in NGC253. We take this to imply a decrease in the efficiency of PAH emission induced by the star formation, caused by mechanical energy input into the ISM or photoionisation or photodissociation of the PAH molecules. All three hypotheses are discussed. In addition, for the first time we present observations of PAH emission in the superwind of a starbursting system (NGC253), providing strong support that winds are heavily mass-loaded and entrain substantial amounts of ambient ISM. We have also found a plausible connection between observed NaD absorption, H2, and PAHs above the plane of NGC253. This observation has important implications for enriching galaxy halos and possibly the intergalactic medium with small dust grains. Comment: A&A Accepted, for a version with higher quality figures see http://www.eso.org/~ltacconi/PAPERS
11/2004;
-
[show abstract]
[hide abstract]
ABSTRACT: We report medium resolution VLT ISAAC K-band spectroscopy of the nuclei of seven ultraluminous infrared galaxies. After accounting for stellar absorption features, we have detected several molecular hydrogen (H_2) v=1-0, 2-1, and 3-2 vibrational emission lines, as well as the HI Br\gamma and HeI 2^1P-2^1S recombination lines. The relative H_2 line intensities show little variation between the objects, suggesting that the H_2 excitation mechanisms in the nuclei are similar in all the objects. The 1-0 emissions appear thermalised at temperatures T\sim1000K. However, the 2-1 and 3-2 emissions show evidence of being radiatively excited by far-ultraviolet (FUV) photons, suggesting that the H_2 excitation in the ULIRGs may arise in dense photon dominated regions (PDRs). We show that the line ratios in the nuclei are consistent with PDRs with cloud densities between 10^4 to 10^5cm^{-3}, exposed to far ultraviolet (FUV) radiation fields at least 10^3 times more intense than the ambient FUV intensity in the local interstellar medium. We have constructed starburst models for the ULIRGs based on their H_2 properties, as well as on the intensities of the recombination lines. Our models provide a consistent picture of young 1-5Myr star clusters surrounded by relatively dense PDRs which are irradiated by intense FUV fluxes. Comparison to the inner few hundred parsecs of the Milky Way indicates that the star formation efficiency in ULIRGs is 10--100 times higher than in the Galactic Center. Comment: accepted by ApJ (32 pages including figures)
07/2003;
-
R. Genzel,
R. Schoedel,
T. Ott,
F. Eisenhauer,
R. Hofmann,
M Lehnert,
A. Eckart,
T. Alexander,
A. Sternberg,
R. Lenzen,
Y. Clenet,
F. Lacombe,
D. Rouan,
A. Renzini, L. E. Tacconi-Garman
[show abstract]
[hide abstract]
ABSTRACT: We analyze deep near-IR adaptive optics imaging as well as new proper motion data of the nuclear star cluster of the Milky Way. The surface density distribution of faint stars peaks within 0.2" of the black hole candidate SgrA*. The radial density distribution of this stellar 'cusp' follows a power law of exponent 1.3-1.4. The K-band luminosity function of the overall nuclear stellar cluster (within 9" of SgrA*) resembles that of the large scale, Galactic bulge, but shows an excess of stars at K<14. We find that most of the massive early type stars at distances 1-10" from SgrA* are located in two rotating and geometrically thin disks. These disks are inclined at large angles and counter-rotate with respect to each other. Their stellar content is essentially the same, indicating that they formed at the same time. The star closest to SgrA* in 2002, S2, exhibits a 3.8 micron excess. We propose that the mid-IR emission either comes from the accretion flow around the black hole itself, or from dust in the accretion flow that is heated by the ultra-violet emission of S2. Comment: 59 pages, 18 figures
05/2003;
-
[show abstract]
[hide abstract]
ABSTRACT: The small separation of the individual stellar components in the TTau system has prevented spectroscopy of the individual components in the near-infrared (NIR) in the past. We present NIR data (H- and K-band) on this object taken using the ALFA adaptive optics (AO) system in combination with the 3D integral field spectrograph. Except for the Brackett series seen in emission, the NIR spectra of \tts{} appear featureless, suggesting that warm dust dominates the radiation. No ro-vibrational lines of molecular hydrogen were found in close vicinity to the stars. The Brackett line emission from \ttn{} and S could not be resolved with the 3.5-m-telescope, implying that it arises within 6 AU from the stars. The line ratios between Br$\gamma$ (2.166 \mum{}) and Br10 (1.736 \mum{}) toward \ttn{} and \tts{} are similar, suggesting similar selective extinctions towards the respective emitting regions. Our results are consistent with a model that describes \tts{} as a pre-main sequence star surrounded by a small edge-on disk, leaving the polar regions relatively unobscured. We present numerical simulations which support this model. Comment: 8 pages, 3 figures, ApJ (March 2002, accepted)
12/2001;
-
[show abstract]
[hide abstract]
ABSTRACT: Progress in understanding the embedded stars in LkHa225 has been hampered by their variability, making it hard to compare data taken at different times, and by the limited resolution of the available data, which cannot probe the small scales between the two stars. In an attempt to overcome these difficulties, we present new near-infrared data on this object taken using the ALFA adaptive optics system with the MPE 3D integral field spectrometer and the near-infrared camera Omega-Cass. The stars themselves have K-band spectra which are dominated by warm dust emission, analagous to class I-II for low mass YSOs, suggesting that the stars are in a phase where they are still accreting matter. On the other hand, the ridge of continuum emission between them is rather bluer, suggestive of extincted and/or scattered stellar light rather than direct dust emission. The compactness of the CO emission seen toward each star argues for accretion disks (which can also account for much of the K-band veiling) rather than a neutral wind. In contrast to other YSOs with CO emission, LkHa225 has no detectable Br_gamma emission. Additionally there is no H_2 detected on the northern star, although we do confirm that the strongest H_2 emission is on the southern star, where we find it is excited primarily by thermal mechanisms. A second knot of H_2 is observed to its northeast, with a velocity shift of -75kms and a higher fraction of non-thermal emission. This is discussed with reference to the H2O maser, the molecular outflow, and [S II] emission observed between the stars. Comment: to appear in ApJ, April 2001. 18 pages, including 6 figures
01/2001;
-
[show abstract]
[hide abstract]
ABSTRACT: One of the most important techniques for astrophysics with adaptive optics is the ability to do spectroscopy at diffraction limited scales. The extreme difficulty of positioning a faint target accurately on a very narrow slit can be avoided by using an integral field unit, which provides the added benefit of full spatial coverage. During 1998, working with ALFA and the 3D integral field spectrometer, we demonstrated the validity of this technique by extracting and distinguishing spectra from binary stars separated by only 0.26". The combination of ALFA & 3D is also ideally suited to imaging distant galaxies or the nuclei of nearby ones, as its field of view can be changed between 1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution we present new results both on galactic targets, namely young stellar objects, as well as extra-galactic objects including a Seyfert and a starburst nucleus.
06/2000;
-
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of gas inflow motions towards the active nucleus of the Circinus galaxy caused by the non-axisymmetric potential of a nuclear gas bar. Evidence for dust associated with the bar comes from the HST/NICMOS H-K color map, whereas the streaming motions along the gas bar are seen in the velocity field of the H2 S(1)(1-0) emission line. The gas bar is about 100 pc long with a visual extinction in excess of 10 mag. Indication for the gaseous nature of this bar comes from the lack of a stellar counterpart even in the K band where the extinction is greatly reduced. We also use the NICMOS emission line images (Pa-alpha, [SiVI], and [FeII]) to study the innermost region of the ionization cones and the nuclear star forming activity. We discuss the possible relationship of these components with the gaseous bar. Comment: 14 pages, 7 figures (3 color plates), accepted for publication in ApJ
10/1999;
-
R. Genzel,
D. Lutz,
E. Sturm,
E. Egami,
D. Kunze,
A. F. M. Moorwood,
D. Rigopoulou,
H. W. W. Spoon,
A. Sternberg, L. E. Tacconi-Garman,
L. Tacconi,
N. Thatte
[show abstract]
[hide abstract]
ABSTRACT: We present an ISO SWS and ISOPHOT-S, mid-infrared spectroscopic survey of 15 ultra-luminous IRAS galaxies. We combine the survey results with a detailed case study, based on near-IR and mm imaging spectroscopy, of one of the sample galaxies (UGC 5101). We compare the near- and mid-IR characteristics of these ultra-luminous galaxies to ISO and literature data of thirty starburst and active galactic nuclei (AGN), template galaxies. We find that 1) 70-80% of the ultra-luminous IRAS galaxies in our sample are predominantly powered by recently formed massive stars. 20-30% are powered by a central AGN. These conclusions are based on a new infrared 'diagnostic diagram' involving the ratio of high to low excitation mid-IR emission lines on the one hand, and on the strength of the 7.7um PAH feature on the other hand. 2) at least half of the sources probably have simultaneously an active nucleus and starburst activity in a 1-2 kpc diameter circum-nuclear disk/ring. 3) the mid-infrared emitting regions are highly obscured. After correction for these extinctions, we estimate that the star forming regions in ULIRGs have ages between 10^7 and 10^8 years, similar to but somewhat larger than those found in lower luminosity starburst galaxies. 4) in the sample we have studied there is no obvious trend for the AGN component to dominate in the most compact, and thus most advanced mergers. Instead, at any given time during the merger evolution, the time dependent compression of the circum-nuclear interstellar gas, the accretion rate onto the central black hole and the associated radiation efficiency may determine whether star formation or AGN activity dominates the luminosity of the system. Comment: 63 pages postscript (ex. MS Word), 11 postscript and 2 gif figures, submitted to ApJ. See also http://www.mpe-garching.mpg.de/ISO/preprint/MPE-IR-97003.html
11/1997;
-
04/1997; 6:48.
-
[show abstract]
[hide abstract]
ABSTRACT: We present a high-resolution (0.6") 2.2 micron (K-band) image of the
central (~750 Pc) circumnuclear region of the starburst galaxy NGC 1808.
Contrary to previous lower resolution observations our image reveals
detailed structure in the distribution of near-infrared light that is
produced within the circumnuclear region. Our data reveal the presence
of many distinct and compact (<~ 0.7") near-infrared continuum
sources spread throughout the circumnuclear region. These sources are
likely individual clusters containing a few to several hundred massive
(~25-30 M_sun_) red supergiants. The inferred cluster masses range from
10^5^ to 10^6^ M_sun_. Together with previous 2.17 micron Brγ line
observations we conclude that the circumnuclear clusters are young and
that their rates of star-formation are decaying rapidly. The cluster
ages are close to the "critical" age of 10 Myr at which clusters reach
their maximum luminosities in the near-infrared. The individual stellar
systems we have detected are probably gravitationally bound. They appear
to be the first unambiguous detections of the IR counterparts of young
clusters (possibly globular clusters) which have recently been
identified in high- resolution optical and ultraviolet (HST) imaging of
several types of starburst galaxies. A 500 pc long infrared bar, and
evidence of inner spiral or ring-like structures are present in our
image. The infrared bar is well aligned with a more extended (~6 kpc)
bar-structure visible in wide-field Hα and 21 cm emission line
maps. A prominent, and just resolved, 2.2 micron continuum source is
present at the galaxy nucleus. Most of the near-infrared light in the
nuclear source is likely produced by massive red giants and supergiant
stars. Both decaying and continuous modes of star formation are
consistent with the observations. For the decaying mode the inferred age
is 8 Myr with a burst mass of ~5 x 10^6^ M_sun_ within the central 50
pc. For continuous star formation the inferred age is ~200 Myr with a
total accumulated mass of 3.2 x 10^7^ M_sun_. Continuous star formation
may be fueled by gas inflow along the bar at a rate of ~0.16 M_sun_
yr^-1^.
The Astronomical Journal 08/1996; 112:918. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present K (2.01-2.42 μm) and H (1.5-1.8 μm) band imaging
spectroscopy of the complex environment of the young stellar object, T
Tau. These observations reveal at least five distinct sources of
molecular hydrogen emission in the central 4×4 arcsec of the
system, including knots of emission centered on the primary and infrared
companion, an east-west jet, and what appears to be a Herbig-Haro object
located within 3" of the binary. We detected the latter object in 11
different quadrupole lines of molecular hydrogen, as well as in two H
band forbidden transitions of Fe II. The H2 spectral line
ratios point to shock heating with a variety of excitation temperatures.
The images also demonstrate that the Brγ emission is point-like
and centered on the primary star only. We discuss the nature and origin
of the line radiation, the relationship between the outflows and the
stars, and the apparent lack of UV fluorescent excited H2.
The Astronomical Journal 05/1996; 111:2403. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present improved 0.15 sec resolution K-band (2.2 micrometers) maps of
the central 0.5 pc of the Galaxy as well as, for the first time, 0.2 sec
J-band (1.25 micrometers) images, 0.2 sec K-band polarimetry, and 0.4
sec images in the 2.058 micrometer He 1 emission and 2.29 micrometers CO
band head absorption features. The new K-band maps reach K magnitudes of
about 16 and resolve the previously found object at the position of the
radio source Sgr A*(R) into a small cluster of compact sources. With one
exception, their polarizations are similar to other sources in its
vicinity and thus are probably caused by antisotropic foreground dust
extinction in the Galactic plane. The Sgr A*(IR) complex does not
exhibit any significant flux density variations at 2.2 micrometers on
timescales of minutes or years. We therefore interpret Sgr A*(IR) as a
small local clustering of luminous stars (MK approximately
equal to -3) near/at the position of the compact radio source. The
central IRS 16 complex and the bright source IRS 13 are dominated by
bright luminous He 1 stars and confirm the cluster of about a dozen He 1
stars found by Krabbe et al. (1991). There are also a dozen sources with
K less than or equal to 12.5 exhibiting CO band head absorption within a
radius of 10 sec of Sgr A*(IR). The drop in CO band head strength found
by Sellgren et al. (1990) thus is most likely not caused by the
disappearance of CO sources but by the additional presence of the bright
early-type stars.
The Astrophysical Journal 04/1995; 445:L23-L26. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: As part of an extensive study of the infrared properties of luminous
galactic nuclei we report here subarcsecond-resolution near-infrared
imaging and spectroscopy of the nucleus of the Seyfert 1 galaxy NGC
7469. Our measurements elucidate for the first time the spatial
distribution of the near-infrared continuum and a number of bright
near-infrared lines (Br gamma, (Fe II), (Si VI), H2, He I, and CO) on a
scale of less than a few hundred parsecs. We find that these tracers
originate from three distinct components: the nucleus, a 1.5 sec (480
pc) radius circumnuclear ring/spiral-arm system with embedded knots, and
a 1 sec ridge of blueshifted, radially streaming gas emanating southward
from the nucleus. The circumnuclear ring is the location of a powerful
starburst deeply embedded in a large concentration of molecular gas and
dust and has a luminosity of approximately 3 x 1011 solar
luminosity, two-thirds of the bolometric luminiosity of the entire
galaxy. It contains a number of supergiant star formation regions with a
few 104 OB stars each. Our 0.4 sec resolution near-infrared
images do not show evidence for a stellar bar. Gas influx into the
nucleus and starburst ring were most likely triggered by greater than or
equal to 108 yr ago by the interaction of NGC 7469 with its
neighbour, IC 5283. A comparison of the mass derived from gas and
stellar dynamics and from the CO 1-0 millimeter line emmision suggests
that the conversion factor from molecular hydrogen column density to
integrated CO flux (X = N(H2)/I(CO)) in the central 800 pc is
significantly smaller than in the Galactic disk, presumably as the
result of the impact of the intense star formation activity on the
surrounding interstellar medium. We have carried out a quantitive
analysis of the ring's visible, infrared, and radio emission using star
cluster models. The data are well fit by two types of solutions. One
possibility is that the star formation rate has been constant
(approximately 30 solar mass/yr) over the last several 107 yr
and stars more massive than 30-40 solar mass have not been forming
during this period. An alternative model that does not require an upper
mass cutoff is a decaying burst with a decay time significantly less
than its present age (approximately 1.5 x 107 yr). For both
star formation histories and for small N(H2)/I(CO) conversion factor
mentioned above, the star formation efficiency in NGC 7469 is high and
the burst is soon going to end because the gas reservoir is exhausted.
Our 2.1 micrometers H2 S(1) line maps show that there is a large
concentration of molecular gas close to the Seyfert 1 nucleus of NGC
7469. The central 102 pc of NGC 7469 contains
108+/-1 solar mass of neutral interstellar gas, consistent
with current unifying models for Seyfert 1 and 2 nuclei. Broad (FWHM
1400 km/s) 1.96 micrometers (Si VI) line emission arises in moderately
dense (n e greater than or equal to 102/cc) gas
within a few 102 pc from the nucleus. Our work clearly shows
that NGC 7469 is a luminous Seyfert galaxy whose total energy output is
predominantly powered by star formation.
The Astrophysical Journal 04/1995; 444:129-145. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: As part of a survey for duplicity among nearby M dwarfs with the
technique of near-infrared speckle imaging we detected two faint
companions to the low-mass star LHS 1070. Apportioning the system
brightness among the main component and the companions of this triple
system, we obtain absolute brightnesses at 2.2 micrometers of
KA=9.27 mag, KB=10.47 mag and KC=10.82
mag. Based on empirical mass-K magnitude relationship for M dwarfs
(Henry & McCarthy 1993), a primary mass of mA=0.099 solar
mass is estimated, while the masses of the companions should be close to
or even slightly below the hydrogen burning limit of 0.08 solar masses.
LHS 1070 has an important advantage over the few still fainter
candidates for substellar masses: orbital motion within this triple
system with its small component separations of a few astronomical units
will allow useful dynamical mass determinations for the companions
within the next few years. The observed changes in relative position of
the components between July 1993 and April 1994 appear compatible with
the photometrically deduced very low component masses.
Astronomy and Astrophysics 10/1994; 291:L47-L50. · 4.59 Impact Factor
